�������� ����� ��

Fluid focusing and its link to vertical morphological zonation at the Dajishanvein-type tungsten deposit, South China

Xiangchong Liu, Huilin Xing, Dehui Zhang

PII: S0169-1368(14)00083-3DOI: doi: 10.1016/j.oregeorev.2014.04.005Reference: OREGEO 1206

To appear in: Ore Geology Reviews

Received date: 5 November 2013Revised date: 30 March 2014Accepted date: 3 April 2014

Please cite this article as: Liu, Xiangchong, Xing, Huilin, Zhang, Dehui, Fluid focusingand its link to vertical morphological zonation at the Dajishan vein-type tungsten deposit,South China, Ore Geology Reviews (2014), doi: 10.1016/j.oregeorev.2014.04.005

This is a PDF file of an unedited manuscript that has been accepted for publication.As a service to our customers we are providing this early version of the manuscript.The manuscript will undergo copyediting, typesetting, and review of the resulting proofbefore it is published in its final form. Please note that during the production processerrors may be discovered which could affect the content, and all legal disclaimers thatapply to the journal pertain.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

*Corresponding author at: School of Earth Sciences and Resources, China University of Geosciences (Beijing),

Beijing 100083, China. E-mail address:zhdehui@cugb.edu.cn, h.xing@uq.edu.au

Fluid focusing and its link to vertical morphological zonation at

the Dajishan vein-type tungsten deposit, South China

Xiangchong Liua,b, Huilin Xingb*, Dehui Zhanga* a. State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences and Resources,

China University of Geosciences (Beijing), Beijing 100083, China

b. Centre for Geoscience Computing, School of Earth Sciences, The University of Queensland, Brisbane, QLD

4072, Australia

Abstract: Five-floor vertical zonation in vein morphology is a common phenomenon

in exo-contact vein-type tungsten deposits of South China and has been widely

applied for practical exploration, but the causative mechanisms are poorly understood.

We combine fractal methods and finite element based numerical analysis to

investigate the link between the fluid focusing and the vertical morphological

characteristics at the Dajishan tungsten deposit and to determine vein growth

mechanisms. Fractal analysis of vein morphology indicates that the growth

mechanisms of veins in the lower part of ore bodies were mainly controlled by growth

rate. Anisotropic permeability tensor method is applied to evaluate the anisotropic

flow behaviours in joints. Numerical experiments on permeability ratio and aspect

ratio controlled by stress state indicate that the NWW-striking joints in the host rock

significantly affect the fluid focusing in these joints and the other potential conduits.

The higher permeability and aspect ratios in the lower levels of the joint systems lead

to the more fluid focusing in the lower part of ore bodies, which delivers more fluids

required for precipitating silica. The five-floor zonation at this deposit is related to the

regional tectonic evolution from the Indosinian (257~205 Ma) to Yanshanian

(205~135 Ma) in South China. This paper may also help to better understand the

vertical morphological zonation in this type of tungsten deposits in China.

Key words: Dajishan; Tungsten; Morphological zonation; Fluid focusing;

Permeability ratio; Aspect ratio.

1. Introduction

Vertical morphological zonation is a common phenomenon at exo-contact

vein-type tungsten deposits in South China (Gu, 1984). Field geologists have

identified five zones based on the vein morphology since 1960s, and proposed a

five-floor vertical morphological zonation. In the five-floor zonation, the top zone is

called thread vein zone where thin veins not over 1 cm in thickness occur. These

barren thin veins gradually become thicker and richer in tungsten downwards,

forming the veinlet zone then mixing zone of veinlet-thick veins. The veins in the

mixing zone converge downwards into a few wolframite-quartz veins often exceeding

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

1 m in thickness, which is called thick vein zone. At the root of the five-floor zonation,

these thick veins shrink downwards and become barren (more details see Clarke

(1983) and Liu and Ma (1993)). The five-floor zonation has played an important role

in prospecting this type of tungsten deposits in the last few decades (Gu, 1984; Mao et

al., 2013; Wang et al., 2010; Xu et al., 2008). However, the reason for such a zonation

is still unclear.

Although vertical morphological zonation is one of the most apparent

characteristics in the vein-type tungsten deposits, South China, it is not well

developed elsewhere. Vein-style tungsten-tin deposits in Cornwall, England and in

Panasqueira, Portugal also show variable vein thicknesses (Foxford et al., 2000; Hall,

1971; Sanderson et al., 2008), but these sheeted vein systems do not exhibit as regular

morphological zonation as those in South China. The distinctive morphological

characteristics of veins in China may indicate complicated coupling of magmatic

hydrothermal processes and regional tectonic evolution (Liu and Ma, 1993; Yu, 2004).

Therefore, it is necessary to better clarify the mechanisms of the five-floor zonation to

understand its links to mineralization and to better target blind deposits.

With regard to hydrogeology, formation of these deposits involved complicated

problems that coupled thermal, hydraulic, mechanical, and chemical processes

(Ingebritsen and Appold, 2012; Zhao et al., 2012). Massive quartz veins at these

deposits require extremely focused flow to deposit silica given its low solubility in

aqueous fluids (Akinfiev and Diamond, 2009; Zhu et al., 1981). Percolation models

suggest that fracture evolution is essential to the locations and styles of tungsten-tin

mineralization, and that the veins tend to develop when localized opening and

channelized flow happens at the backbones of fracture systems (Roberts et al., 1998,

1999; Sanderson et al., 2008). This means that focused flow in fractures is one of the

necessary conditions to account for the morphological zonation. Analytical solutions

(Zhao et al., 2006, 2008) demonstrate that fluid focusing in joints or faults depends on

their hydraulic characteristics (permeability ratio) and geometric characteristics

(aspect ratio).

In this paper, we firstly present the geological background of the Dajishan

tungsten deposit. Then, we illustrate vein thickness distribution at this deposit using

fractal techniques, which characterize its morphological characteristics improving that

described by Liu and Ma (1993). These fractal methods can trace the history of vein

growth and help understand the use of morphological zonation in exploration. These

data and observations are used as constraints on the numerical modeling. Next, we

numerically investigate fluid flow and heat transfer using an anisotropic permeability

tensor. Numerical experiments indicate that permeability and aspect ratios

significantly influence the degree and location of fluid focusing in oriented joints.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

Finally, we build a link between the focused flow in the existing joints and the vertical

morphological zonation constrained by fractal methods.

2. Background

The Dajishan tungsten deposit, located in Quannan County, Jiangxi Province, is a

large-scale vein-type and granite-type tungsten polymetallic deposit. The vein-type

deposit discovered in 1917 has a WO3 reserve of 160,000 tonnes with an average

grade of 2.04% (Mao et al., 2013). The ore deposit lies in the Nanling Range of the

Cathaysian Block that is situated inboard from the subduction zone of the Western

Pacific plate (Fig.1a). Recent data suggest that tungsten concentration of stream

sediments in the Cathaysian Block is 5~250 times the Clark value (0.6 ppm) of crust

in East China (Chi et al., 2012). The Yanshanian (205~135Ma) was the most

important epoch for magmatic activity in South China (Zhou et al., 2006). Mesozoic

granites are present throughout this region, consisting of Jurassic granites mainly

distributed in the Nanling Range and in the interior of South China tectonic block and

Cretaceous granites along the present-day continental margin (Zhou et al., 2006).

Almost all of the polymetallic tungsten deposits in Jiangxi were related to Yanshanian

granites and formed at the endo- or exo-contact of granite intrusions (Guo et al., 2011;

Mao et al., 2013).

The exposed strata include Cambrian, Devonian, and Paleogene rocks (Fig.1b).

The Cambrian strata consist of low-grade metamorphic sandstone and slate that hosts

the Dajishan granite and ore body. These sedimentary rocks strike 300o~320

o and dip

20o~40

o. The Devonian strata consist of coarse sandstone, phyllite, and quartz

conglomerate, strike 30o~50

o and dip 40

o~80

o. The contact relationship between the

Devonian and Cambrian units is an angular unconformity (Zhou, 2009).

The main structure at the Dajishan deposit is a synclinorium with a NE-striking

axis and four groups of structural elements, divided by their orientations: EW, NE,

NNE, and NWW structures (Fig.1c). The EW structures include an EW silification

belt in the contact between the Wuliting granite and the host rock, quartz porphyry

filled in an EW fault and No.14 EW vein in the ore body. The NE structures include

the Dajishanfeng Fault (F5) and the Chuandiwo Fault (F1-F4). The NNE-trending

structures consist of small-scale compressive faults in mineralized area. A few faults

in this group are filled with tungsten-bearing quartz veins, although most are small

faults that cut the ore body. The NWW-striking structures include the ore-bearing

fractures and a fault filled with diorite (Zhou, 2009).

Magmatic rocks in the ore district include biotite granite, two-mica granite,

muscovite granite, diorite, and quartz porphyry (Fig.1). The Wuliting biotite granite is

dated at 238.4±1Ma by the zircon U-Pb method (Zhang et al., 2004), whereas its

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

whole-rock Rb-Sr age is 167±1Ma (Sun, 1989) and its biotite K-Ar age is

160.3±3.0Ma and 164.2±3.5Ma (Jiang et al., 2004). The two-mica granite occurring

below the ore body is dated at 161Ma by the whole-rock Rb-Sr isochron (Sun, 1989)

and at 160.6±2.8Ma by the muscovite K-Ar method (Jiang et al., 2004). The

muscovite granite occurs from the level of 517m to 0m. It consists of five small

intrusions, of which the No.69 granite is the largest and Ta-Nb-W-Be mineralized

(Fig.1d). The whole-rock Rb-Sr age of the No.69 granite is 159±5Ma (Sun, 1989),

while its zircon U-Pb age is 151.7±1.6Ma (Zhang et al., 2006). Drill data indicate that

the muscovite granite was intruded later than the two-mica granite. The diorite is the

host rock of the vein-type ore body at the middle set. The quartz porphyry swarm

occurs in the Cambrian strata, but its age is unknown. Geophysical data show that the

Dajishan ore district is situated above EW-trending blind granite with an area of

several thousand km2 (Zhou, 2009).

The tungsten-bearing quartz veins occur in the Cambrian metamorphic sandstone,

slate, and diorite. Alteration of wall rock include silicification, tourmalinization, and

biotitization in sandstone, greisenization in the granite, and biotitization in the diorite

(Sun, 1989). Ore minerals include wolframite, scheelite, tungstite, bismuthinite, native

Bi, and molybdenite, and gangue minerals are quartz, feldspar, muscovite, calcite, and

tourmaline. The typical minerals in the middle vein set are orthoclase, microcline,

perthite, and albite (Zhou, 2009).

The age of mineralization at the Dajishan vein-type deposit is 160±1.3 Ma dated

by the molybdenite Re-Os isochron (Zhang et al., 2011) and 144 Ma and 147 Ma by

the muscovite 40

Ar-39

Ar method (Zhang et al., 2006). Hydrogen and Oxygen isotopic

measurements (δ18

O=9.9~11.5‰, D=-75.1~-60.7‰) in the three types of granite

suggest that they were formed by crustal anatexis, and the fluids were derived from

magmatic water (Zhuang et al., 1991). The ore-forming fluids are interpreted to be

magmatic in the main mineralization stage, and then were mixed with meteoric waters

in a late stage (Zhang et al., 1997). Based on oxygen isotope mineral pairs (quartz and

wolframite, quartz and scheelite, and quartz and mica), mineralization temperatures

were 300~400oC (Zhang et al., 1997). Infrared measurements suggest that the fluid

inclusions in wolframite experienced relatively simple evolution history and had

higher temperature range than those in quartz (Ni et al., 2006). The mineralized fluids

were in the H2O-NaCl system or in the H2O-CO2-CH4-NaCl system (Wang et al.,

2013; Xi et al., 2008). Homogenization temperatures of inclusions in quartz are

200~330oC, and salinities are typically 4~10wt% (Wang et al., 2013; Xi et al., 2008).

The fluid pressure at the time of mineralization is estimated to be 114~132MPa,

indicating that the ore-forming depth was 4.6~5.3km (Xi et al., 2008).

Fig.2 shows the spatial zonation of the granites and veins along with the

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

interpreted relative timing of granite and vein emplacement. The

magmatic-hydrothermal system is interpreted to be multi-phrase from a magmatic to

post-magmatic period (Kong, 1982; Teng, 1990), with both the spatial and temporal

distributions the consequence to tectonic activity. At the Dajishan vein-type deposit,

silicates and oxides are present in the upper part of vein systems, whereas oxides,

sulfides, and carbonates are dominant in the lower part (Teng, 1990).

3. Geological structures

Previous studies suggest that the mineralization at the deposit was controlled by

fractures (Liu and Yu, 2009; Zhou, 2009), and therefore the structural characteristics

of joints and faults are summarized below. Joint numbers and orientations were

measured on a line transect normal to vein orientation. A geochemical profile through

the Dajishanfeng Fault was measured at 467m level to constrain fluid flow and heat

transfer therein.

3.1. Joints

Previous studies indicate that two sets of preferred orientated joints occur at this

deposit, and their azimuths are 9o 74

o and 181

o 66o, respectively (Zhou, 2009; see

Fig.3a). The definition of the azimuth is dip direction dip angle. The corresponding

principal stresses are 252o 79

o (σ1), 95

o 11o (σ2), and 5

o 4o

(σ3) (Zhou, 2009). The

joints dipping north are more abundant than those dipping south. The mineral and

associated alteration assemblages in one set show no difference from the other. The

preferred orientations of joints we measured show a similar result to the previous

studies (Fig.3b). Our measurements also indicate that vein density increases with

increasing joint density (Fig.4).

3.2. Faults

The Dajishanfeng Fault and Chuandiwo Fault are situated in the east and in the

west of ore-bearing veins, respectively. The Dajishanfeng Fault outcrops near the

unconformity between the Cambrian and Devonian strata, trending 50o and dipping

40o~60

o NW. It consists of compressive fracture zones and reverse faults without

obvious strike-slip movement. Previous studies indicate that the barren Dajishanfeng

Fault predates mineralization as it is cut by veins both at 467m and at 985m levels

(Zhou, 2009). The geochemical profile through this fault at 467m level indicates that

rock type changes from hornfels to meta-sandstone, and that quartz veins become

fewer and thinner from DP1-1 to DP1-12 (Fig.5). Along the profile, grades of WO3

fall from 1156 ppm to 10 ppm with a significant rise at the eastern side of the fault.

These data indicate this fault played a minor role in mineralization. Previous studies

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

suggest that the Chuandiwo Fault also shows little control on formation of

mineralized veins (Zhou, 2009).

3.3. Veins

The ore-bearing veins are divided into three vein sets by their locations: the north

set, the middle set, and the south set. The south and north sets occur in the Cambrian

strata, whereas the middle set mainly occurs in the diorite. The vein sets extend

horizontally 300~650 m with the eastern end close to the Dajishanfeng Fault. Most

veins trend 280o~300

o and dip 65

o~80

o NNE (Zhou, 2009). The ore bodies are

wedge-shaped, and numerous thin veins converge to a few thick veins downwards

(Fig.6).

In section 4, we characterize the vertical morphological zonation using the data

of vein morphology. In section 6 and 7, we conduct numerical simulations using the

data of structures.

4. Morphological characteristics of veins

The middle and north sets were chosen as the objects in this study. The middle

set becomes barren at 517m and wedges out at 267m, whereas the north set extends to

the level of 100m (Fig.1d). The two-mica granite present below the middle and north

sets occurs at the level of 240m and 100m, respectively (Zhou, 2009). Using the

classification of the five-floor zonation (Fig.4 in Liu and Ma, 1993), the middle set

between the 467m and 317m levels represents the fifth zone of the vein system, i.e.

the thin out zone, and the north set between the 467m and 317m levels represents the

fourth zone, i.e. the thick vein zone.

Fifteen horizontal traverses normal to veins were chosen to measure vein

thickness, length, and density in the middle and north sets (Fig.1d; Table 1). True vein

thickness has been transformed from the value measured along scan lines by vein’s

dip angle. The minimum vein thickness recorded was 1.0 cm. Data of vein length in

the middle set were not successfully obtained due to inadequate exposure.

4.1. Methods

The distribution of vein thickness is a useful tool for characterizing fracture

evolution and fluid channelization in vein-style deposits (André-Mayer and Sausse,

2007; Gillespie et al., 1999; Monecke et al., 2001; Sanderson et al., 2008). Given that

fractal-geometry techniques have been widely applied to quantify rock structures

(Kruhl, 2013), these fractal methods were applied to describe the morphological

characteristics of the vein systems at the Dajishan deposit.

Similar to other non strata-bound vein systems, both power law and

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

negative-exponential distributions were compared to identify vein thickness

distribution. Power law distribution follows the function (Gillespie et al., 1999):

, (1)

Negative exponential distribution follows the function (Sanderson et al., 2008):

, (2)

where N(t) is the number of objects of size t or larger, t represents vein thickness, and

Dt is the fractal dimension of thickness. Low values of Dt mean that there is a large

proportion of thick veins compared to thin ones (Gillespie et al., 1999).

The relationship between vein thickness and length infers the segment linkage of

vein system. Their relation is generally expressed by (Gillespie et al., 1999):

, (3)

where t is the vein thickness, L is the vein length, and c is the power-law exponent.

Vein systems evolve from isolated veins to interacting veins through segment linkage

(Kim and Sanderson, 2005), increasing the value of c.

4.2. Results

Fig.7 and Table 2 show the fitted distributions of vein thickness and the related

parameters. For the north set, the distribution of vein thickness at 317m is ambiguous

due to large fit goodness in both power law (R2=0.92) and negative exponential

(R2=0.97) distributions, whereas vein thickness at 467m level conforms to a power

law distribution. Veins at 317m level have smaller fractal dimension (the slope of the

fitted line) than those at 467m level either for negative exponential distribution or for

power law distribution. For the middle set, vein thickness at both levels conforms to

power law distributions. Veins at 317m have larger fractal dimension than the ones at

467m. For power law distribution, the middle set has a smaller average fractal

dimension than the north set.

Veins at 317m level in the north set have smaller power-law exponent n than the

ones at 467m level (Table 2).This result was fitted by 10 pairs of thickness-length data

at both levels.

4.3. Vein growth mechanisms

The channelized fluid flow through fractures is often explained by a percolation

model (Sanderson et al., 2008) or by a stochastic model (Monecke et al., 2001). In the

percolation model, a percolation threshold is the critical point, above which

well-linked fractures characterized by decreasing Dt and increasing c allow focused

flow through part of the fracture system (Sanderson et al., 2008). In the stochastic

model, Dt follows the function (Monecke et al., 2001):

(4)

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

rn is the nucleation rate defined as the number of newly created veins in a unit time

and a unit volume, and rg is the growth rate defined as the increment of vein thickness

in a unit time. A high nucleation rate rn produces a large fractal dimension Dt, whereas

a high growth rate rg yields a small Dt. Combination of these two models might help

to better understand vein growth mechanisms (André-Mayer and Sausse, 2007).

Data of veins in Table 1 and fractal dimensions of power law distribution in

Table 2 were chosen to make the following comparisons. Dt<1 in the two sets

indicates that the systems are above the threshold and well connected. The north set at

317m level has smaller Dt than the same set at 467m level, therefore characterized by

a relative high amount of thick veins. This is consistent with higher growth rate

represented by larger vein thickness and lower nucleation rate reflected by smaller

vein density at 317m level; therefore, vein morphology in the north set between 467m

and 317m levels was controlled by increasing growth rate and decreasing nucleation

rate downwards. This combined contribution reduced Dt in the north set from 467m to

317m level.

Two lines of evidence were used to explain the growth mechanisms of veins in

the north set. One line is the average strain (Table 1). High strain in the vein system at

317m level is interpreted to be linked to large growth rate, compared to that at 467m

level. The other is the power-law relationship between vein thickness and length

(Table 2). Comparison of power-law exponent c implies that the vein system at 317m

level evolved to a higher level of linkage and allowed more focused flow, therefore

increasing the vein growth rate and decreasing the fractal dimension of vein thickness.

The middle set at 317m level has a larger fractal dimension than at 467m level

(Table 2), meaning a smaller proportion of thick veins. This trend of fractal dimension

is ascribed to growth rate rather than nucleation rate. The vein system at 317m level

has a smaller average thickness but a slightly lower average vein density than at 467m

level. This means that the decrease of growth rate from 467m to 317m level

contributes to the increase of fractal dimension, to a large degree. This downward

trend of growth rate is consistent with the downward decrease of average strain (Table

1).

4.4. Vertical morphological zonation

The fractal methods above illustrate a number of morphological characteristics of

the vein system at the Dajishan deposit.

1. It is characterized by decreasing Dt downwards in the fourth zone, represented by

the north set between 317m and 467m levels.

2. It is characterized by increasing Dt downwards in the fifth zone, represented by the

middle set between 317m and 467m levels.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

3. The middle set at 467m level has the smallest Dt among the four groups of data.

Based on limited data, we concluded a rough trend of Dt that first decreases from

the top zone to the fourth zone, then increases in the fifth zone. Veins between the

fourth and the fifth zone have the lowest Dt, implying the most focused fluid flow.

Growth rate controlled the vein growth in the fifth zone, and both growth rate and

nucleation rate determined the vein thickness distribution in the fourth zone. Vertical

morphological zonation derived from the trend of Dt is that numerous thread veins

become thick downward, increasing the proportion of thick veins, then converge to a

few large veins that eventually shrink at the contact zone between the two-mica

granite and the host rock. Therefore, the five-floor zonation can be well characterized

by fractal dimension of vein thickness.

These characteristics of veins are closely related to magmatic hydrothermal

transition that controlled development of quartz veins in time (Liu and Ma, 1993; Zhu

et al., 1981). Reverse mineral zonation implies that multiple stages of mineralization

were focused at different levels, the main mineralization stage in the middle and the

upper parts and the late stage in the lower part. Despite the complexity,

well-crystallized wolframite that is common in thick veins (Fig.3a) suggests that this

morphological zonation, to a large degree, was formed during the main mineralization

stage. This highlights the close relationship between vein’s morphology and tungsten

mineralization.

Similar morphological zonation has also been discovered in epithermal deposits

(Brathwaite et al., 2001) and porphyry deposits (André-Mayer and Sausse, 2007).

These studies indicate that understanding morphological characteristics of veins can

aid in exploration. In vein-type tungsten deposits, the reason why the five-floor

zonation has become a useful prospecting method can be explained in part by the

fractal dimension of vein thickness. The decrease of fractal dimension at the Dajishan

deposit’s north set between 467m and 317m level means the increase of the proportion

of thick veins. This trend predicts the occurrence of channelized flow and much

potential of mineralization at depth. The increase of fractal dimension in the middle

set between 467m and 317m level implies that the degree of fluid focusing falls and

veins might become barren. These predictions in the north and middle sets are

consistent with the resource potential. It can be seen that fractal methods combined

with the five-floor zonation can play a helpful role in exploration.

Despite its important role in exploration, the five-floor zonation has many

uncertainties and limits because it is an empirical prospecting method rather than a

typical metallogenic model involving process understanding (Wang et al., 2010; Xu et

al., 2008). In the next part, we investigate the factors affecting the link between fluid

focusing and the vertical morphological zonation using the finite element method.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

5. Computational models

5.1. Computational model and governing equations

PANDAS, a novel finite element and/or Lattice Boltzmann method (FEM/LBM)

based software, has been developed to simulate highly coupled systems involving

heterogeneously fractured geomaterials to address the key scientific and technological

challenges in geo-science and –engineering at different spatial and temporal scales by

using supercomputers (Xing, 2013; Xing et al 2010). PANDAS has been applied to

simulate crustal dynamics, fault systems and enhanced reservoir systems across

different scales for underground geoenergies (Xing 2013, 2014; Xing and makinouchi

2002; Xing and Mora 2006; Xing et al 2007; Xing et al 2010). It is applied here to

simulate the transient thermal-fluid flow process, and the governing equations are

briefly listed below (Xing, 2014).

For the conservation of non-deformable rock mass with constant porosity , the

continuity equation is expressed as

(5)

where is the fluid velocity; P is the fluid pressure; is the effective

compressibility; is the density; is the porosity. Bold symbols are used for vector

and tensor/matrix variables throughout this paper.

The relationship of fluid velocity and pressure P for fluid flow though porous

media is normally expressed by Darcy’s law:

(6)

where k is the intrinsic permeability tensor of the porous media; g is the gravitational

acceleration; is the dynamic viscosity; D is the depth.

From the energy conservation, the conductive-convective heat transfer in porous

media can be described as:

(7)

, where , is density, C is specific heat capacity,

and subscript r, f, and m denote rock matrix, fluid, and mixture, respectively; heat

conductivity ; T is the temperature; is the energy source

term.

5.2 Anisotropic permeability tensor method

Permeability is often anisotropic in geologic systems (Rosenberg et al., 1993),

and is strongly controlled by rock fabric (Ingebritsen and Appold, 2012). In

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

intrusion-related deposits, permeability is however strongly controlled by fracture

networks (Titley, 1990). Anisotropic permeability of these fractures is often described

by a permeability tensor (Oda, 1985), an equivalent continuous method to model fluid

flow in petroleum and hydrological studies (Snow, 1969). The permeability tensor in

a set of parallel fractures is defined as (Gupta et al, 2001):

(8)

It assumes that all of the fractures have smooth parallel plane walls of infinite extent.

The permeability scalar k accounts for the anisotropic intensity that fractures bring to

the porous media. The unit permeability tensor accounts for the directional effect

in the fluid flow due to fractures in the medium. The unit permeability tensor is

defined as:

(9)

where stand for the orthogonal axes , and ; is the Kronecker delta,

vanishing when and unity when ; is the component of the vector

normal to the fracture plane. The function of is defined by:

(10)

where is the dip direction of fractures, the dip angle. The permeability scalar

is defined as:

(11)

where is the fracture aperture, and a dimensionless constant. The value of

approaches the upper limit , when the fracture system behaves more like parallel

plate conduits. The fracture density f is defined by f=N/H, where N represents the

number of fractures in a sample volume, H the length of a representative line that

crosses the sample volume. The permeability tensor becomes a diagonal matrix, and

the values in the diagonal line are the principal permeability.

6. Numerical modeling of fractures at the deposit

A geometric model has been built along the section line A-A’ (Fig.8). The

Dajishangfeng Fault and Chuandiwo Fault were omitted in the model given their

minor roles in minerlization. Most ore-bearing veins have similar orientations to the

preferred oriented joints, particularly the set dipping north. This implies that these

oriented joints may become potential conduits for mineralized fluids, therefore were

incorporated in the model. The joint system consists of five parts (Є-3 to Є-7) with the

same size, corresponding to the five zones (Є-3 the fifth zone and Є-7 the first zone).

The contact zone (Є-1) refers to the Cambrian strata and early crystallized granite

given multiple magmatic activities. The boundary and initial conditions are shown in

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

Fig.8.

6.1. Hydraulic parameters

The permeability tensor of oriented joints was calculated using equation (8)~(10)

(Appendix A). The diagonalized unit permeability tensor is:

(12)

The major axis (k11=1.0) is on the intersection of the two sets and trends NWW, the

minor (k33=0.3) bisects the obtuse angle of the two sets and strikes NNE, and the

intermediate (k22=0.7) bisects the acute angle and is along the vertical dimension

(Fig.9). The coordinate system in simulations is NNE as X-axis, NWW as Y-axis, and

the vertical dimension as Z-axis. X-axis is perpendicular to the oriented joints, Y-axis

along oriented joints. The 2D model in Fig.8 corresponds to X-Z plane and invokes

k22 and k33.

Both the joint aperture and density are required to compute the permeability

scalar k. Aperture that controls permeability scalar of joints varies during the

evolution of hydrothermal systems (Ingebritsen and Manning, 2010). It is also

difficult to know if joints are connected or unconnected. For simplicity, the

permeability’s order of magnitude is constrained by the depth-dependent permeability

(Ingebritsen and Manning, 2010):

(13)

where k is in m2 and Z in km. Mineralization depth is estimated to be ~5 km (Xi et al.,

2008), so the permeability’s order of magnitude is approximately 10-16.7

m2. Existing

quartz veins imply that this value might be a lower limit for the jointed host rock.

Diorite is the host rock for the middle set, and field measurements show that joint

density here is slightly higher than the one in the north set but equal to the value in the

south set (Fig.6). Given the slight difference in joint density between the diorite and

the Cambrian strata, we did not differentiate between the diorite and the Cambrian

strata in the models.

6.2. Key assumptions

Several assumptions have been made to focus the models on the short period of

time when magmatic fluids were released. First, several lines of evidence indicate that

high permeability is localized in the upper crust and has a limited lifetime, ranging

100~10

3 years (Ingebritsen and Manning, 2010). This short-lived high permeability is

the key to form ore deposits (Cathles and Shannon, 2007; Ingebritsen and Appold,

2012; Liu, 2011; Lupi et al., 2011; Weatherley and Henley, 2013), and therefore

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

numerical experiments were run for no more than 1000 years. Permeability of all units

was assumed to be fixed and was not changed as a result of thermo-mechanical stress

and chemical precipitation (Germanovich and Lowell, 1992; Lowell et al, 1993).

Second, fluid inclusions in wolframite or in quartz are mainly two-phase

aqueous-rich (Cao et al., 2009; Song et al, 2011; Wang et al., 2007; Wang et al., 2009,

2013; Wei et al., 2012; Xi et al., 2008), implying that boiling was not the dominant

mechanism controlling mineralization in this type of deposits (Wang et al., 2011).

Given this constraint, we assumed that the release of magmatic fluids was driven by

constant overpressure during a short period, neglecting thermal expansion of fluids

and fluid production in wall rocks (Hanson, 1995). Fluid inclusion analysis at the

Dajishan deposit also suggests that lithostatic pressures were reached (Xi et al., 2008),

and that a pressure gradient approximating 105Pa/m existed over 1 kilometer. In this

case, the effect of the gravity term (104Pa/m) in equation (6) was ignored.

Third, the contact zone is considered to be permeable at about 600oC. In

magmatic hydrothermal systems, brittle-ductile transition (BDT) exists around the

contact zone (Fournier, 1999). Recent numerical simulations employing

temperature-dependent permeability indicate BDT is defined at 650~750oC (Coumou

et al., 2009), higher than 350~400oC constrained by Fournier (1999). Generally, the

BDT depends on temperature as well as mineralogy and strain rate (Fournier, 1999;

Ingebritsen, 2012; Simpson, 2001). For simplicity, we consider the contact zone Є-1

as permeable rock when magmatic volatiles were expelled.

6.4. Models

Fluid focusing in joints depends on both the permeability ratio of joints to host

rock and the aspect ratio of long axis to short axis (Zhao et al., 2006, 2008). We

conducted four numerical experiments to illustrate the link between fluid focusing and

the five-floor zonation. In experiment 1, permeability in each unit is isotropic and

each part of the joint system has the same permeability and aspect ratios. This ideal

case acts as a reference experiment. In experiment 2, we investigated how

permeability ratio influences fluid focusing in the joint system. In this experiment, we

did not follow the assumption of an infinitely extended fracture plane in permeability

tensor, because joints in geological environments are not always connected in all

directions. Previous numerical simulations indicate that the maximum connectivity

often occurs in the direction of maximum principle stress (Sanderson and Zhang, 1999;

Zhang and Sanderson, 2001). The maximum principle stress during mineralization

was almost vertical (Zhou, 2009), so we elevated the vertical permeability and

increased the permeability ratio and the degree of anisotropy. In experiment 3, we

studied how geometric characteristics of the joint system affect fluid flow therein. The

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

width of the vein set decreases downwards (Liu and Ma, 1993; Zhou, 2009), implying

the lower part of the joint system has larger aspect ratio than the other parts.

Experiment 4 was conducted to examine the combined influence of permeability ratio

and aspect ratio. We displayed the output in 1 year to represent a transient result and

the one in 20 years to represent the steady state.

7. Simulation results

7.1 Experiment1

Hydraulic parameters are shown in Table 3. After 1 year, a large pressure

gradient occurred in the lower part of joint system, driving fluids flow into the joint

system (Fig.10a, b). In the upper part, fluids moved outwards due to high fluid

pressure relative to the host rock. Fluid moved fastest (9.4╳10-8

m/s) in the lower part

of joint system. After 20 years, the pressure gradient and fluid velocity has decreased

relative to 1 year (Fig.10c, d), the maximum velocity decreasing to 8.2╳10-8

m/s, and

flow was mainly focused in the third zone (Є-5). Table 4 shows that pressure

distributions in all four experiments have reached steady state after 20 years. For

convenience, velocity ratio is defined as the ratio of maximum velocity in any

experiment to the maximum in experiment 1 after 20 years. This parameter was used

to highlight the difference between this experiment and the following experiments

(Table 4).

7.2. Experiment 2

Previous studies using convection-type models have shown the significant

impact of anisotropy on flow patterns and heat transfer (Dutrow et al., 2001; Gerdes et

al., 1998; Hurwitz et al., 2002, 2003; López and Smith, 1996; Rosenberg et al., 1993).

In this experiment, porosity and vertical permeability of the fourth and fifth zones was

also increased to 0.14 and 7.0╳10-14

m2, respectively. After 1 year, the pressure

gradient around these two parts was much higher than experiment 1, causing faster

flow in fourth and fifth zones (Fig.11a, b). After 20 years, fluid flow became slightly

slower than before but was still most focused in fourth zone with a velocity ratio of

1.3 (Fig.11c, d, Table 4).

7.3. Experiment 3

We reduced the width of the fourth and fifth zones from 150m to 60m, raising

their aspect ratios from 2 to 5. All units have the same hydraulic parameters as

experiment 1. After 1 year, one large pressure gradient was generated around these

two zones, moving fluids towards them (Fig.12a, b). After 20 years, pressure gradient

in these areas became lower, decreasing fluid velocity therein, and fluids were most

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

focused in the fourth zone, not in the fifth zone anymore (Fig.12c, d). The velocity

ratio decreased from 1.9 after 1 year to 1.6 after 20 years.

7.4. Experiment 4

We adopted the same geometric size of joint system as that of experiment 3 and

the same hydraulic parameters as that of experiment 2. Thus, the fourth and fifth

zones have higher aspect ratio and higher permeability than the other zones. This

experiment has the hydraulic and geometric characteristics closest to those of the

Dajishan tungsten deposit, compared to the other experiments. After 1 year, flow

velocity in the fifth zone increased rapidly upwards, reached its peak in the fourth

zone, and then decreased gradually upwards (Fig.13a, b). In the steady state after 20

years, the fourth zone still had larger pressure gradient and higher degree of fluid

focusing than other zones (Fig.13c, d). The velocity ratios in this experiment are

higher than the one in any other experiments.

8. Discussions

8.1. Comparisons with analytical solutions

Fluid focusing in joints has been positively correlated with permeability ratio and

aspect ratio (equation 23 in Zhao et al., 2006). The interaction of these two parameters

implies that fluid focusing is related to an increment of one parameter as well as to the

current value of the other (Zhao et al., 2006). These conclusions, together with

comparisons between experiment 1 and others (Table 4), were used to test the

numerical results.

In experiment 1, fluids were focused in the joint system due to a permeability

ratio greater than 1. This is consistent with one conclusion from the analytical

solutions that a permeability ratio larger than 1 is a prerequisite for fluid focusing in

joints. In experiment 2, elevating vertical permeability of the fourth and fifth zones is

equivalent to increasing the permeability ratio. An increase of flow velocity is

consistent with a positive correlation between fluid focusing and permeability ratio. In

experiment 3, the high aspect ratio in the lower part of the joint system led to

accelerated flow, which is in agreement with the analytical solutions. In experiment 4,

high permeability ratio and aspect ratio in the fourth and fifth zones exerted the most

significant influence on fluid focusing in joints. This is consistent with the nonlinear

relationship of the analytical solutions. The comparisons above suggest that the

numerical experiments match well with the analytical solutions.

8.2. Insights from simulations

The nature of the initial fracture system is of vital importance to the subsequent

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

development of vein-style mineralization (Sanderson et al., 2008). Numerical

experiments suggest that the NWW-striking joints acted the main pathways

channelizing fluids. In experiment 1, fluid flow was most focused in the third zone

after a short geological time. However, this ideal case does not agree with the

constraint from fractal methods that fluid flow was most concentrated between the

fourth and the fifth zone. Increasing the permeability ratio (experiment 2) or aspect

ratio (experiment 3) in the fourth and fifth zones improved the degree of fluid

focusing and lowered the focusing location. Experiment 4 indicates that increasing the

permeability ratio and aspect ratio in the fourth and fifth zones together had the most

significant impact on fluid flow. In this case, fluid flow was most focused in the fourth

zone, therefore allowing for the greatest potential to transfer heat and mass. This

implies that high permeability and aspect ratios in the lower part of the joint system

are a necessary but an insufficient condition for precipitating quartz in the fourth

zone.

Permeability and aspect ratios in the joint system are closely related to stress

state during mineralization. Previous numerical models (Sanderson and Zhang, 1999;

Zhang and Sanderson, 2001) indicate that loading direction exerts an important

influence on deformation, and that only those fractures parallel to maximum principle

stress remain open. Hence, the maximum principle stress that was vertical during

mineralization improved the connectivity of subvertical NWW-striking joints,

therefore increasing their permeability ratio. Those models also suggest that enhanced

fluid flow is extremely localized in small areas of the fracture network when a critical

stress state is reached. Fluid pressure in the lower part of the joint system was much

higher than the upper part, allowing it to reach the critical stress state easily. If so,

fluid flow would be highly localized in a few large fractures. This localization of

deformation in the lower part of the deposit corresponds to a high aspect ratio. For the

upper part of the joint system, it is relatively difficult to reach the critical state due to

low fluid pressure. This leads to uniformly distributed apertures and low flow velocity.

In this case, the aspect ratio in the upper part was lower than in the lower part.

Therefore, fluid focusing influenced by permeability ratio and aspect ratio is

essentially controlled by the coupling of mechanical deformation and fluid flow.

8.3. Control of regional structure

The orientations of vein-style tungsten-tin deposits are controlled by granite

emplacement and crystallization or by external stress regimes (Černý et al., 2005). In

this part we focus on the relationship between regional tectonic evolution and the

approximate EW-striking joints.

Regional tectonic stress, as the intermediate principle stress, is interpreted to

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

have controlled the joint orientation at the Dajishan tungsten deposit (Zhou, 2009).

There is also a general agreement that this preferred orientation of ore-bearing

structures in the same type of deposits in South China was controlled by regional

tectonic evolution from the Indosinian (257~205 Ma) to Yanshanian (205~135 Ma)

(Liu and Ma, 1993; Mao et al, 2013; Zhou, 2009). During the Indosinian epoch,

widespread EW-striking folds and thrusts in the Nanling Range were formed in a N-S

compressive stress regime dominated by the Tethyanorogenic domain, and resulted in

nucleation of approximate EW-trending joints; In the Yanshanin epoch, regional stress

regime was changed to a WNW-ESE compressive stress regime controlled by

paleo-Pacific tectonic domain (Wan, 2012), which may have played a role in further

propagation of EW-trending mechanical weakness (Wan, 2012). This tectonic

evolution is supported by the time-space distribution of Mesozoic granitoids (Zhou,

2006) and tungsten-tin ore deposits in South China (Mao et al, 2013). Without the

influence of regional structure, it is difficult to explain the vein-type tungsten deposits

that were formed within the short time of 160-150Ma in South China (Mao et al,

2013), over 90% of which trend approximate EW (Zhu et al, 1981). Note that the

vein-type tungsten deposits having morphological zonation can occur in the strata

from the Sinian to Jurassic and in many types of sedimentary and magmatic rocks (Gu,

1984). Additionally, granite related to these deposits is F-rich and B-poor (Chen et al.,

1989; Zhang et al., 2004). Without these oriented joints, F-bearing magma often

creates disseminated rather than vein-style mineralization due to low amount of

mechanical energy released during crystallization (Pollard et al, 1987). These

constraints imply that regional structure played an important role in controlling

large-scale distribution of vein-type tungsten deposits in South China.

8.4. Limitations

Vein thickness data in the other three zones are absent because the upper part of

the vein sets is inaccessible. This constrains the trend of fractal dimension to a narrow

range. Also, the morphological characteristics do not incorporate vein spacing, an

important parameter to infer the link between vein clustering and fluid focusing

(Gillespie et al., 1999). Due to the inadequate data, the vertical morphological

zonation we illustrated is not a full map of the five-floor zonation, but it is an

important part of it.

One deficiency of using the permeability tensor is the assumption of infinite

fractures (Gupta et al., 2001), which neglects the connectivity of the joint networks.

Actually, only a small part of connected joints dominate fluid transport (Taylor et al.,

1999). This implies that a better tool incorporating connectivity structure (Renard and

Allard, 2013) is important to model hydrodynamic processes of mineralization.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

Numerical simulations only dealt with fluid flow in the joint system.

Temperature played a minor role due to its front much slower than pressure front and

limited time. To improve the model, it is necessary to further investigate fluid flow

coupled with other physical and chemical processes in the vein-type tungsten deposits.

In this case, permeability is not constant any more, but varies as physical properties of

rock are changed by deformation, temperature, and chemical reactions.

9. Conclusions

Using the five-floor zonation terminology, the chosen data in the middle set

represents the fifth zone, and the data in the north set correspond to the fourth floor.

Fractal methods suggest that the growth mechanisms of veins in the fourth and fifth

zones were mainly controlled by growth rate. The fractal dimension of vein thickness

indicates that the proportion of thick veins increases downwards in the fourth zone,

but decreases in the fifth zone. Therefore, the degree of fluid focusing would have

greatest between the fourth and the fifth zone. These insights improve on the use of

the five-floor zonation for exploration.

A Permeability tensor was used to model anisotropic permeability of oriented

joints at the Dajishan tungsten deposit. Numerical experiments based on the finite

element method suggest that NWW-striking joints in the host rock acted potential

conduits for mineralized fluids. Consistent with the analytical solutions, two

parameters have an impact on fluid focusing in these joints, permeability ratio and

aspect ratio. High permeability and aspect ratio in the lower part of the joint system

favors fluids focusing in the fourth zone, allowing the necessary fluids to precipitate

silica. Thus, the favorable condition for forming the five-floor type deposits is high

permeability and aspect ratio in the lower part of the joint system relative to higher

areas, a condition controlled by stress state during mineralization.

The origin of these orientated joints is related to regional tectonic evolution from

the Indosinian to Yanshanian in South China. These conclusions reached by the fractal

methods and numerical experiments present a clue to understand the vertical

morphological zonation in this type of deposits in this region.

Acknowledgements

The work is financially supported by the NSFC grant (41373048) and the MLR

special research fund (201411024). Xiangchong Liu also acknowledges the

scholarship from the CSC and the financial support from the GPMR Open Project

Program (NGPMR2011). We would like to thank Liqiang Yang, Shide Mao,

Yongquan Li, Zhiwei Tian, Huaizhong Yu, Jinfang Gao, Yan Liu, Nianchao Zhang,

Quanshu Li, and Paul D. Bons for helpful advices and discussions, as well as the

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

staffs of the Dajishan Tungsten Company in field work. David Polya is appreciated

for presenting his paper about wolframite solubility. Xiangchong Liu thanks Chunxi

Lu for her continuing encouragement and appreciates the help of Bo Zhao, Rongzhen

Zhang. The related calculation was carried out by using PANDAS software on the

savanna supercomputer at UQ. We also thank Dr Peter Schaubs of CSIRO Earth

Science and Resource Engineering and an anonymous reviewer for their constructive

comments and advice to improve the manuscript significantly.

Appendix A

The unit permeability tensor of two sets of joints is as follows:

and are the unit permeability tensors of the first set of joints (9o 74

o) and

the second one (181o 66

o), respectively, and and are the corresponding

weighting coefficients. Their values calculated by equation (9)~(10) are:

,

,

References

André-Mayer, A.-S., Sausse, J., 2007. Thickness and spatial distribution of veins in a porphyry copper

deposit, Rosia Poieni, Romania. J. Struct. Geol. 29, 1695-1708.

Akinfiev, N.N., Diamond, L.W., 2009. A simple predictive model of quartz solubility in

water–salt–CO2 systems at temperatures up to 1000°C and pressures up to 1000MPa. Geochim.

Cosmochim. Acta 73, 1597-1608.

Brathwaite, R.L., Cargill, H.J., Christie, A.B., Swain, A., 2001. Lithological and spatial controls on the

distribution of quartz veins in andesite- and rhyolite-hosted epithermal Au–Ag deposits of the

Hauraki Goldfield, New Zealand. Mineral. Deposita 36, 1-12.

Cao, X.F., Lu, X.B., He, M.C., Niu, H., Du, B.F., Mei, W., 2009. An infrared microscope investigation

of fluid inclusions in coexisting quartz and wolframite : a case study of Yaogangxian quartz vein

wolframite deposit. Mineral Deposits Chin. 28(5): 611-620. (In Chinese with English Abstract)

Cathles, L.M., Shannon, R., 2007. How potassium silicate alteration suggests the formation of

porphyry ore deposits begins with the nearly explosive but barren expulsion of large volumes of

magmatic water. Earth Planet. Sci. Lett. 262, 92-108.

Černý, P., Blevin, P.L., Cuney, M., London, D., 2005. Granite-related ore deposits. Society of

Economic Geologists 100th Anniversary, 337-370.

Chi, Q.H., Wang, X.Q., Xu, S.F., Zhou, J., Liu, H.L., Liu, D.S., Zhang, B.M, Wang, W., 2012.

Temporal and spatial distribution of tungsten and tin in South China Continent. Front Earth Sci.

Chin. 19(3): 70-83. (In Chinese with English abstract)

Clarke, M.C.G., 1983. Current Chinese thinking on the South China tungsten province. Trans. Inst.

Min. Metall., Sect. B 92, 10-15.

Coumou, D., Driesner, T., Geiger, S., Paluszny, A., Heinrich, C.A., 2009. High-resolution

three-dimensional simulations of mid-ocean ridge hydrothermal systems. J. Geophys. Res. 114.

Dutrow, B.L., Travis, B. J., Gable, C. W., Henry, D. J., 2001. Coupled heat and silica transport

associated with dike intrusion into sedimentary rock: effects on isotherm location and permeability

evolution. Geochim. Cosmochim. Acta 65, 3749-3767.

Fournier, R.O., 1999. Hydrothermal processes related to movement of fluid from plastic into brittle

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

rock in the magmatic-epithermal environment. Econ. Geol. 94, 1193-1212.

Foxford, K.A., Nicholson, R.A., Polya, D.A., Hebblethwaite, R.P.B, 2000. Extensional failure and

hydraulic valving at Minas da Panasqueira, Portugal. J. Struct. Geol. 22, 1065-1086.

Gerdes, M.L., Baumgartner, L.P., Person, M., 1998. Convective fluid flow through heterogeneous

country rocks during contact metamorphism. J. Geophys. Res. 103, 23983-24003.

Germanovich, L.N., Lowell, R.P., 1992. Percolation Theory, Thermoelasticity, and Discrete

Hydrothermal Venting in the Earth's Crust. Science 255, 1564-1567.

Gillespie, P.A., Johnston, J.D., Loriga, M.A., McCaffrey, K.J.W., Walsh, J.J., Watterson, J., 1999.

Influence of layering on vein systematics in line samples. Geol. Soc. London Spec. Publ. 155,

35-56.

Gu, J.Y. 1984. Morpholgical zonation of tungsten deposits in South China. In: Yu, H.Z. (ed.). Proc.

Symposium Tungsten Geology (Chinese edition), Nanchang, 1981. Beijing: Geological Publishing

House, 35-45 (in Chinese).

Guo, C., Mao, J., Bierlein, F., Chen, Z., Chen, Y., Li, C., Zeng, Z., 2011. SHRIMP U–Pb (zircon),

Ar–Ar (muscovite) and Re–Os (molybdenite) isotopic dating of the Taoxikeng tungsten deposit,

South China Block. Ore Geol. Rev. 43, 26-39.

Gupta, A., Penuela, G., Avila, R., 2001. An Integrated Approach to the Determination of Permeability

Tensors for Naturally Fractured Reservoirs. J. Can. Pet. Technol. 40, 43-48.

Hanson, R.B., 1995. The hydrodynamics of contact metamorphism. Geol Soc Am Bull 107, 595-611.

Hall, A., 1971. Greisenisation in the granite of Cligga Head, Cornwall. P GEOLOGIST ASSOC 82,

209–230.

Hurwitz, S., Ingebritsen, S.E., Sorey, M.L., 2002. Episodic thermal perturbations associated with

groundwater flow: An example from Kilauea Volcano, Hawaii. J. Geophys. Res. 107.

Hurwitz, S., Kipp, K.L., Ingebritsen, S.E., Reid, M.E., 2003. Groundwater flow, heat transport, and

water table position within volcanic edifices: Implications for volcanic processes in the Cascade

Range. J. Geophys. Res. 108, 2557.

Ingebritsen, S.E., Geiger, S., Hurwitz, S., Driesner, T., 2010. Numerical simulation of magmatic

hydrothermal systems. Rev. Geophys. 48, 1-33.

Ingebritsen, S.E., Manning, C.E., 2010. Permeability of the continental crust: dynamic variations

inferred from seismicity and metamorphism. Geofluids 10, 193–205.

Ingebritsen, S.E., 2012. Modeling the Formation of Porphyry-Copper Ores. Science, 338(6114):

1551-1552.

Ingebritsen, S.E., Appold, M.S., 2012. The physical hydrogeology of ore deposits. Econ. Geol.

107, 559-584.

Jiang, G.H., Hu, R.Z., Xie, G.Q., Zhao, J.H., Tang, Q.L., 2004. K-Ar ages of plutonism and

mineralization at the Dajishan tungsten deposit, Jiangxi Province, China. Acta Mineral. Sinica. 24(3),

253-256. (In Chinese with English abstract)

Kim, Y.-S., Sanderson, D.J., 2005. The relationship between displacement and length of faults: a

review. Earth Sci. Rev. 68(3-4): 317-334.

Kong, Z.Q., 1982. Investigation on metallogenic regularity in Dajishan tungsten deposit. Geol Explon 6,

27-43. (In Chinese)

Kruhl, J.H., 2013. Fractal-geometry techniques in the quantification of complex rock structures:

A special view on scaling regimes, inhomogeneity and anisotropy. J. Struct. Geol., 46(0): 2-21.

Liu, Y.J., Ma, D.S., 1993. Vein-type tungsten deposits of China and adjoining regions. Ore Geol. Rev.

8, 233-246.

Liu, N.Q., Yu, C.W, 2009. Complexity of ore-controlling fracture system of Dajishan tungsten deposit,

China. Front Earth Sci. Chin.16, 320-325.

Liu, L.M., 2011. Fluid overpressure and rock fracturing caused by shallow intrusion and their

constraints on hydrothermal mineralization. Front Earth Sci. Chin. 18(5), 78-89. (In Chinese with

English abstract)

López, D.L., Smith, L., 1996. Fluid flow in fault zones: Influence of hydraulic anisotropy and

heterogeneity on the fluid flow and heat transfer regime. Water Resour. Res. 32(10): 3227-3235.

Lowell, R.P., Cappellen, P.V., Germanovich, L.N., 1993. Silica Precipitation in Fractures and the

Evolution of Permeability in Hydrothermal Upflow Zones. Science 260, 192-194.

Lupi, M., Geiger, S., Graham, C.M., 2011. Numerical simulations of seismicity-induced fluid flow in

the Tjörnes Fracture Zone, Iceland. J. Geophys. Res., 116(B7): B07101.

Mao, J., Yanbo, C., Maohong, C., and Pirajno, F., 2013. Major types and time–space distribution of

Mesozoic ore deposits in South China and their geodynamic settings: Mineral. Deposita 48(3),

267-294.

Monecke, T., Gemmell, J.B., Monecke, J., 2001. Fractal distributions of veins in drill core from the

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

Hellyer VHMS deposit, Australia: constraints on the origin and evolution of the mineralising

system. Mineral. Deposita, 36(5): 406-415.

Ni, P., Huang, J., Wang, X., Jiang, S., Ling, H., 2006. Infrared fluid inclusion microthermometry on

coexisting wolframite and quartz from Dajishan tungsten deposit, Jiangxi province, China.

Geochim. Cosmochim. Acta 70(18, Supplement): A444.

Oda, M., 1985. Permeablity tensor for discontinuous rock masses. Géotechnique 35(4), 483-495.

Pollard, P. J., Pichavant, M., and Charoy, B., 1987. Contrasting evolution of fluorine- and boron-rich

tin systems: Mineral. Deposita 22(4) 315-321.

Renard, P., Allard, D., 2013. Connectivity metrics for subsurface flow and transport. Adv. Water Res.

51(0): 168-196.

Roberts, S., Sanderson, D.J., Gumiel, P., 1998. Fractal analysis of Sn-W mineralization from Central

Iberia. Econ. Geol. 93: 360-365.

Roberts, S., Sanderson, D.J., Gumiel, P., 1999. Fractal analysis and percolation properties of veins.

Geol. Soc. London Spec. Publ., 155(1): 7-16.

Rosenberg, N.D., Spera, F.J., Haymon, R.M., 1993. The relationship between flow and permeability

field in seafloor hydrothermal systems. Earth Planet. Sci. Lett., 116(1–4): 135-153.

Sanderson, D.J., Zhang, X., 1999. Critical stress localization of flow associated with deformation of

well-fractured rock masses, with implications for mineral deposits. Geol. Soc. London Spec. Publ.,

155(1): 69-81.

Sanderson, D.J., Roberts, S., Gumiel, P., Greenfield, C., 2008. Quantitative Analysis of Tin- and

Tungsten-Bearing Sheeted Vein Systems. Econ. Geol. 103, 1043-1056.

Sheldon, H.A., Ord, A., 2005. Evolution of porosity, permeability and fluid pressure in dilatant faults

post-failure: implications for fluid flow and mineralization. Geofluids 5, 272-288.

Simpson, F., 2001. Fluid trapping at the brittle–ductile transition re-examined. Geofluids, 1(2):

123-136.

Snow, D.T., 1969. Anisotropie Permeability of Fractured Media. Water Resour. Res. 5(6),

1273-1289.

Song, S.Q., Hu, R.Z., Bi, X.W., Wei, W.F., Shi, S.H., 2011. Fluid inclusion geochemistry of Taoxikeng

tungsten deposit in southern Jiangxi Province, China. Geochimica 40(3), 237-248. (In Chinese with

English abstract)

Sun, G.A., 1989. Dajishan tungsten, niobium, and tantalum deposit in Jiangxi Province. In Chen YC et

al, ed., The Geology of Nonferrous and Rare Metal Deposits Related to Mesozoic Granitoids in

Nanling Range, China. Beijing, Geological Publishing Housing, 74-87. (In Chinese)

Taylor, W.L., Pollard, D.D., Aydin, A., 1999. Fluid flow in discrete joint sets: Field observations and

numerical simulations. J. Geophys. Res. 104, 28983-29006.

Teng, J.D.,1990. Vertical zoning of mineralization in the Dajishan Mine. Mining Geology, 11(2):13-24.

(In Chinese)

Titley, S.R., 1990. Evolution and Style of Fracture Permeability in Intrusion-Centered Hydrothermal

Systems. In: Geophysics Study Committee, N.R.C. (Ed.), The Role of Fluids in Crustal Processes.

The National Academies Press, Washington, D.C., pp. 50-63.

Wan, T.F., 2012. The Tectonics of China. Springer Berlin Heidelberg, pp. 149-196.

Wang, D., Lu, H.Z., Bi, X.W., 2011. Comparison of characteristics of ore forming fluids between

quartz-vein tungsten deposits and porphyry copper deposits associated with granitic rocks. Front

Earth Sci. Chin. 18(5), 121-131. (In Chinese with English abstract)

Wang, D.H., Tang, J.X., Ying, L.J., Chen, Z.H., Xu, J.X., Zhang, J.J., Li, S.R., Zeng, Z.L., 2010.

Application of Five levels + Basement model for prospecting deposits into depth. J Jilin Univ (Earth

Science Edition) 40(4): 733-738. (In Chinese with English abstract)

Wang Q.Y., Hu, R.Z., Peng, J.T., Bi, X.W., Wu, L.Y., Liu, H., and Su, B.X. Charactersitics and

significance of the fluid inclusions from Yaogangxian tungsten deposit in south of Hunan. Acta

Petrol Sin Acta, 2007, 23(9), 2263-2273.

Wang, X.D, Ni, P., Jiang, S., Zhao, K., Wang, T., 2009. Origin of ore-forming fluid in the Piaotang

tungsten deposit in Jiangxi Province: Evidence from helium and argon isotopes. Chin. Sci. Bull.

55(7): 628-634.

Wang, X.D., Ni, P., Yuan, S.D., Wu, S.H., 2013. Fluid inclusion studies of Dajishan tungsten deposit

in Jiangxi Province. Mineral Deposits Chin. 32, 308-322. (In Chinese with English abstract)

Weatherley, D.K., Henley, R.W., 2013. Flash vaporization during earthquakes evidenced by gold

deposits. Nature Geosci. 6(4): 294-298.

Wei, W.F., Hu R.Z., Bi, X.W., Peng, J.T., Su, W.C., Song, S.Q., Shi, S.H., 2012. Infrared

microthermometric and stable isotopic study of fluid inclusions in wolframite at the Xihuashan

tungsten deposit, Jiangxi province, China. Mineral. Deposita, 47(6): 589-605.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

Xi, B.B., Zhang, D.H., Zhou, L.M., Zhang, W.H., Wang, C., 2008. Characteristics of ore-forming fluid

evolution in Dajishan tungsten deposit, Quannan County, Jiangxi. Acta Geol. Sin. 82(7), 956-966.

Xing, H.L., & Makinouchi, A., 2002. Three dimensional finite element modelling of thermomechanical

frictional contact between finite deformation bodies using R-minimum strategy, Comput. Methods

in Appl.Mech.Eng 191, 4193-4214.

Xing, H. L., Mora, P., 2006. Construction of an intraplate fault system model of South Australia, and

simulation tool for the iSERVO institute seed project. PAGEOPH. 163, 2297-2316.

Xing, H.L., Makinouchi, A.,Mora, P., 2007. Finite element modeling of interacting fault system, Phys.

Earth Planet. In. 163, 106-121.

Xing, H.L., J. Gao, J., Zhang, J. & Liu, Y., 2010. Towards an integrated simulator for Enhanced

Geothermal Reservoirs. Proceedings World Geothermal Congress 2010, Indonesia, 25-29.

http://www.geothermal-energy.org/pdf/IGAstandard/WGC/2010/3224.pdf

Xing, H.L., 2013. PANDAS - A highly coupled nonlinear simulator got multiscale geocomputing.

User’s Manual Version 1.0, The University of Queensland

Xing, H., 2014. Finite element simulation of transient geothermal flow in extremely heterogeneous

fractured porous media. J. Geochem. Explor. , http://dx.doi.org/10.1016/j.gexplo.2014.03.002

Xu, J.X., Zeng, Z.L., Wang, D.H., Chen, Z.H., Liu, S.B., Wang, C.H., Ying, L.J., 2008. A new type of

tungsten deposit in southern Jiangxi and the new model of ‘five floors+basement’ for prospecting.

Acta Geol. Sin. 82(7), 880-887. (In Chinese with English abstract)

Yu, C.W., 2004. Fractal dilation of multiple hydraulic fracturing. Front Earth Sci. Chin. 11(3), 11-44.

(In Chinese with English abstract)

Zhang, G.X., Xie, Y.N., Yu, F.J., Zhang, H.B., 1997. Stable isotope geochemistry of distinct

metallogenic stages of tungsten deposits in Dajishan mine, Jiangxi. Acta Geosci. Sini. 18,

197-199. (In Chinese with English abstract)

Zhang, X., Sanderson, D.J., 2001. Evaluation of instability in fractured rock masses using numerical

analysis methods: Effects of fracture geometry and loading direction. J. Geophys. Res., 106(B11):

26671-26687.

Zhang, D.H., Zhang, W.H., Xu, G.J., 2004. The ore fluid geochemistry of F-rich silicate melt-hydrous

fluid system and its metallogeny: the current status and problems. Front Earth Sci. Chin.11(2),

479-490. (In Chinese with English abstract)

Zhang, J., Xing, H.L, 2012. Numerical modeling of non-Darcy flow in near-well region of a

geothermal reservoir. Geothermics 42, 78-86.

Zhang, S.M., Chen, Z.H., Shi, G.H., Li, L.X., Qu, W.J., Li, C., 2011, Re-Os isotopic dating of

molybdenite from Dajishan tungsten deposit in Jiangxi Province. Mineral Deposits Chin. 30(6),

1113-1121. (In Chinese with English abstract)

Zhang, W.L., Hua, R.M., Wang, R.C., Li, H.M, Chen, P.R., 2004. Single zircon U-Pb isotopic age of

the Wuliting granite in Dajishan area of Jiangxi, and its geological implication. Acta Geol. Sin.

78(3), 352-358. (In Chinese with English abstract)

Zhang, W.L., Hua, R.M., Wang, R.C., Chen, P.R., Li, H.M., 2006. New dating of the Dajishan granite

and related tungsten mineralization in South Jiangxi. Acta Geol. Sin. 80(7), 956-962. (In Chinese

with English abstract)

Zhao, C.B., Hobbs, B.E., Ord, A., Peng, S.L., Liu, L.M., Mühlhaus, H.B., 2006. Analytical solutions

for pore-fluid flow focusing within inclined elliptic inclusions in pore-fluid-saturated porous rocks:

solutions derived in an elliptical coordinate system. Math Geol 38(8): 987-1010.

Zhao, C., Hobbs, B., Ord, A., Peng, S., Liu, L., 2008. Inversely-mapped analytical solutions for flow

patterns around and within inclined elliptic inclusions in fluid-saturated rocks. Math Geol 40(2):

179-197.

Zhao, C.B, Reid, L.B., Regenauer-Lieb, K., 2012. Some fundamental issues in computational

hydrodynamics of mineralization: A review. J. Geochem. Explor. 112, 21-34.

Zhou, X.M., Sun, T., Shen, W.Z., Shu, L.S., Niu, Y.L., 2006. Petrogenesis of Mesozoic granitoids and

volcanic rocks in south China : a response to tectonic evolution. Episodes. 29, 26-33.

Zhou, L.M., 2009. Numerical modeling of paleo-tectonic stress field and metallogenic prognosis in

Dajishan tungsten deposit, Quannan, Jiangxi. Master dissertation. Beijing: China University of

Geosciences (Beijing), p.67. (In Chinese with English abstract)

Zhu, Y.L., Li, C.Y., Lin, Y.H., 1981. Tungsten deposit geology in South Jiangxi Province. Nanchang:

Jiangxi People’s Publishing House, 1-440. (In Chinese)

Zhuang, L.C., Lin, W.S., Xie, T.H., 1991. Stable isotope geochemistry of the Dajishan tungsten mine in

Jiangxi Province. Bulletin of the YiChang Institute of Geology and Mineral Resources Chinese

Academy of Geological Sciences 16, 109-120. (In Chinese with English abstract)

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

Fig.1. (a) A simplified map showing the tectonic units in the South China Block (modified from Guo et

al, 2011); (b) Regional geological map of the Dajishan tungsten deposit (Sun et al., 1985); (c), (d)

Plane map and cross section map of the Dajishan tungsten deposit, respectively (modified from Sun et

al., 1989)

1-fault; 2-reverse fault; 3-indeterminated fault; 4-geological boundary; 5-unconformity;

6-tungten-bearing quartz veins; 7-location of the sample lines of measuring vein morphology;

-granite; - two-mica granite;

-muscovite granite; -granite-porphyry; -quartz porphyry;

-diorite; Q-Quaternary; E-Paleogene; K-Cretaceous; J-Jurassic; C-Carboniferous; D-Devonian;

Є-Cambrian; A-A’ in Fig.1c is the cross-section line for Fig.1d and is also used in the numerical model.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

Fig.2 Schematic pattern of diagenesis and mineralization at theDajishan deposit (Kong, 1982)

I-Biotite granite; II-Two-mica granite; III1-Muscovite granite; III2-Stockscheiders; III3-Quartz phrase;

IV1- Microcline quartz veins; IV2- Beryl quartz veins; IV3-Wolframite quartz veins

Fig.3 Rose diagrams of dip direction of joints at theDajishan tungsten deposit

(a). 446 joint orientations were measured from the level of 317m to 985m by Zhou (2009). (b). To

supplement the data in Zhou (2009), 32 joint orientations were measured from the level of 267m to

467m. Both two diagrams show that the set of joints that dips NNE is more abundant than the one

dipping SSW.

Fig.4 Vein density increases with joint density. The data were measured at three levels, 467m, 317m,

and 267m. The average joint density is 0.83/m, and the average vein density is 0.42/m. The average

joint density in the north set is 0.67/m, 0.98/m both in the middle and in south sets.

a b

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

Fig.5 (a) A simplified map of the deposit at level 467m. It shows the relative location of DP1 to the

deposit. DP1 lies at 467m level. (b) The geochemical profile DP1 and its related geological cross

section. It starts with east of the middle set and strikes 110o, covering 220m. DP1-1 is the starting point.

Blocky and fragmented hornfels occurs in 0-55m, where 2-6cm thick quartz veins trend 5-12o and dip

75o, occurring wolframite and sulfide. In 55-74m, hornfels is well fragmented and has 1cm thick quartz

veins that strike approximate E-W. The fracture zone is the Dajishanfeng Fault. In 74-220m,

metamorphic sandstone is silicified and few barren quartz veins occur. Grades of WO3 drop from 1156

ppm at DP1-1 to 10 ppm at DP1-12.

Fig.6 (a). Euhedral wolframite often occurs in thick veins, the photo taken at 417m level in the north

set with a hammer as the scale. The morphology of wolframite implies that fracture aperture was large

and was held open for enough time for crystal growth; (b) Parallel thread veins (<1 cm in thickness)

outcrop at 985m level (Zhou, 2009). Veins in (a) and (b) trend NWW.

Wolframite Thread veins a b

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

Fig.7 Vein thickness distributions

(a)-(b) are fitted power law distribution and negative exponential distribution for vein thickness in the

north set, respectively. (c)-(d) are fitted power law distribution and negative exponential distribution for

vein thickness in middle set, respectively. Fractal dimensions of thickness are the fitted slopes.

Fig.8 The geometry model used in the numerical simulations

The location of cross section A-A’ is shown in Fig.1c. It trends NNE, normal to the vein sets. The

Z-axis represents the paleodepth. Є-1 stands for the contact zone, and joint system consists of Є-3, Є-4,

Є-5, Є-6, and Є-7, corresponding to the fifth floor to the first floor. Each part of the joint system is

0.3km high and 0.015 wide, the same aspect ratio of 2. Magmatic fluids are released from the top of

magma. The boundary conditions include 100oC and 40Mpa at top and 600

oC and 170MPa at the top of

magma. The right and left sides have free boundary conditions.

a b

c d Power law distribution Negative exponent distribution

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

Fig.9 The principle permeability in the coordinate system used in the simulations

Fig.10 Numerical results in Experiment 1. (a), (b) Distribution of fluid pressure and flow velocity after

1 year; (c), (d) Distribution of fluid pressure and flow velocity after 20 years. The arrows show the

direction of fluid flow. The unit of pressure is Pa, and the unit of velocity is m/s.

b

a

After 1 year

Maximum: 9.4╳10-8

m/s

After 20 years

c

d

Maximum: 8.2╳10-8

m/s

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

Fig.11 Numerical results in Experiment 2. (a), (b) Distribution of fluid pressure and flow velocity after

1 year; (c), (d) Distribution of fluid pressure and flow velocity after 20 years.

Fig.12 Numerical results in Experiment 3. (a), (b) Distribution of fluid pressure and flow velocity after

1 year; (c), (d) Distribution of fluid pressure and flow velocity after 20 years.

b

a

After 1 year

Maximum: 1.4╳10-7

m/s

After 20 years

c

d

Maximum: 1.1╳10-7

m/s

b

a

After 1 year

Maximum: 1.5╳10-7

m/s

After 20 years

c

d

Maximum: 1.3╳10-7

m/s

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

Fig.13 Numerical results in Experiment 4. (a), (b) Distribution of fluid pressure and flow velocity after

1 year; (c), (d) Distribution of fluid pressure and flow velocity after 20 years.

Table 1 Database of veins in the middle and north sets

Vein

set Level(m) Section Length(m)

Vein

number

Vein

density(/m) Strain (%)

Average

strain (%)

Average vein

density (/m )

Average vein

thickness (m)

Middle

set

467

1 47 23 0.49 8.37

9.25 0.47 0.19 2 20 11 0.55 3.83

3 22 6 0.27 4.91

4 15 9 0.58 19.91

317

5 29 14 0.48 6.20

3.92 0.39 0.10 6 17 6 0.35 4.63

7 23 8 0.35 0.93

North

set

467

8 30 12 0.40 4.64

4.00 0.43 0.08 9 74 34 0.46 2.82

10 50 22 0.44 4.54

317

11 14 6 0.43 5.16

4.59 0.26 0.21

12 27 7 0.26 4.28

13 37 7 0.19 3.13

14 37 8 0.22 5.42

15 32 6 0.19 4.95

b

a

After 1 year

Maximum: 2.0╳10-7

m/s

After 20 years

c

d

Maximum: 1.6╳10-7

m/s

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

Table 2 Summary of the results from fractal methods

Vein set Level (m) Dt-Power Dt-Negative c R2

North

set

467 0.92 7.82 0.91 0.51

317 0.85 4.20 1.14 0.59

Middle

set

467 0.78 3.81

317 0.86 6.19

Dt-Power represents the fractal dimension of power law distribution, Dt-Negative represents

the fractal dimension of negative exponential distribution; R2 is the fit goodness of power-law

relationship between vein thickness and length.

Table 3 Hydraulic parameters in experiment 1

Unit Magma Є-1 Є-2 Є-3,Є-4,Є-5,Є-6,Є-7

kx (m2) 1.0╳10

-18 1.0╳10

-16 2.0╳10

-16 3.0╳10

-15

kz (m2) 1.0╳10

-18 1.0╳10

-16 2.0╳10

-16 3.0╳10

-15

Φ 0.0015 0.015 0.02 0.05

The porosity and permeability are cited from Sheldon and Ord (2005). The density and dynamic

viscosity of fluid are 1╳103 Kg

.m

-3 and 1.3╳10

-4 Pa

.s, respectively. The specific heat capacity of fluid

and rock are 1000 J.kg

-1.K

-1 and 4200 J

.kg

-1.K

-1, respectively. The thermal conductivity of fluid and rock

are 0.6 W.m

-1.K

-1 and 2.0 W

.m

-1.K

-1, respectively.

Table 4 Results of the four numerical experiments

Numerical Experiment 1 2 3 4

Pressure increment during 50

days after 20 years <7Pa <16Pa <6Pa <16Pa

Velocity ratio after 1 year 1.1 1.4 1.9 2.4

Velocity ratio after 20 years 1.0 1.3 1.6 2.0

Pressure change during 50 days indicates that the four experiments reached steady state, given that the

pressure gradient after 20 years is approximately 105Pa/m.

ACC

EPTE

D M

ANU

SCR

IPT

ACCEPTED MANUSCRIPT

Highlights

1. Many vein-type tungsten deposits in China have vertical morphological zonations.

2. We build a link between fluid focusing and the morphological zonation.

3. Permeability ratio and aspect ratio influence the fluid focusing in joints.

4. Fractal analysis on vein morphology helps the use of the zonation in exploration.

Graphical Abstract

Fractal analysis of vein morphology at the Dajishan tungsten deposit, South China

indicates that the lower part has a relative high amount of thick veins, and that the

growth mechanisms of veins in the lower part of ore bodies were mainly controlled by

growth rate. The existing oriented joints above granite became the main pathways for

mineralized fluids. The higher permeability and aspect ratios in the lower levels of the

joint systems lead to the more fluid focusing in the lower part of ore bodies, which

delivers more fluids required for precipitating silica.