hammond textures

7/27/2019 Hammond Textures

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Quartz textures - potential clues toposition and or process in LS systems

Primary Growth Textures

chalcedonic, saccharoidal,comb,zoned crystals, colloform, crustiform

Recrystallisation Textures

Moss, microplumose

Replacement Textures

Mold, Bladed


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Forms of Silica and Quartz

S

Amorphous Silica

Lacks crystalline structure

Cryptocrystalline SilicaCrystals too small to distinguish under normal microscopeegs chalcedony - agate (banded chalcedony)-opal

CrystallineNeedle

Prismatic

Equant

Aqueous silica concentrations are directly influenced by presence ofsolid silica phases (AMORPHOUS / CHALCEDONY / QUARTZ) andtemperature. In long lived sytems quartz controls silica solubility >1800Cand chalcedony controls silica solubility


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Buchanan/Morrison/Corbett & Leach


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Buckskin Mt

After Vikre 1985


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Broadlands Geothermal

broad_geotherm.ppt


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Vera Nancy - Textural Paragenesis


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Champagne Pool and sinter


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Champagne PoolAmorphous silica /mineralised ooze

80 ppm Au

175 ppm Ag

2%As

2%Sb320 ppm Tl

170 ppm Hg


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White Sinter Terraces Waimangu


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Sinter - Waiotapu NZ


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Columnar Growth Structures

perpendicular to Sinter Laminations


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Mud cracks in sinter near Ivanhoe


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Chalcedonic silicaGwenivere Hg Mine (Ivanhoe)


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Coarse carbonate-mold replacement -amorphous silica (Calcatreu)


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Lattice Bladed CarbonateReplacement Texture - Ovacik

Indicative of boiling


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Red Bluff MidasLattice Bladed Texture



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Geothermal Pipe Scale


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Colloform chalcedonic silica, gold,sulphide, adularia (Hishikari)

82405g/t Au 34400 g/t Ag


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Midas colloform high grade with latticebladed bands



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Hishikari Colloform = Gingurofine silica-adularia-sulphide



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Vein Textural Relationships

Faure et al 2002


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Simpson et al 1995 describe apparent sedimentary textures such as grading o

sulphides/quartz plus ripple marks in banded vertical veins at Golden Cross NZ.

Banding within the quartz veins is primarily a result of variation in quartz grain sizeSulphide minerals and kaolinite are most abundant in fine grained quartz bands thamay have been deposited in an amorphous silica state.

These NZ workers interpret observed textures in the following way.

System pressure is breached by fault dilation or hydrothermal eruption resulting inamorphous silica saturation of a rapidly moving fluid. This event is accompanied byupward surge of sulphide rich fluid from deeper in the system. As system pressureresumes via mineral deposition in veins, temperature increases and silica saturationlevels return toward quartz. Eventually the higher T/P system deposits sulphide barren

quartz from more slowly moving fluid.

Repeated system rupturing leads to formation of banded veins.

Banding and Sedimentary textures in Veins


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Schematic Relationship Quartz Grain Size

and Sulphide/Kaolinite Abundance

From Simpson et al 1995

Grain sizes


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Fluid flow textures

in vein from Waihi


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Pajingo Scott Lode - Moss texture

Recrystallisation of silica gel globules


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Crustiform banding-Adularia stained

(Sodium Cobaltinitrite Solution)


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Needle Adularia Mold


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Bonanza Ore Karangahake withcrustiform comb quartz


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Victoria LepantoComb Quartz - crustiform banded


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Calcatreu Terminal brecciasingle phase crystalline quartz


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Amethyst - Vera Nancy Pajingo

Indicative of vapour phase?

Sacharroidal drusy quartz


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Sacharroidal drusy quartz

Generally associated with late hydrothermal activity


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Temperature Overlap

Quartz and Chalcedony

Faure et al 2002


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Multiphase Breccia (Wirralie Qld)


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Cockade texture (Calcatreu V49)

Useful Textures


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Sinter- marks paleo-surface and paleo-watertable. Textures distinguish

from silicified tuff or lake sediment. NB. no Sinter in HS environment.

Chalcedony - low temperature silica (120o-200oC) usually at shallowdepths above an upflow zone and possibly overlying mineralisation.

Colloform banding -in chalcedonic quartz-kidney like or rounded externalsurface from original silica gel. Close association with ore.

Downgrade potential if these textures dont carry grade.

Crystalline quartz -usually occurs in deeper/ hotter part of system at

> 180oC though the temperature overlap between quartz and chalcedony

means both can occur in same part of a vein.

Crystalline Quartz alone likely indicates hot/deep environment > 250oC.

Drusy cavities - void spaces partly filled with terminated crystals(calcite or quartz) are commonly last vestiges of hydrothermal activity.

Lattice textures are indicative of boiling conditions.

Cockade and comb textures - indicate open space filling.

Useful Textures


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By careful observation a great deal can be learnt about

processes operating and likely spatial relationships to ore.

hammond textures

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