Examination of Dr Palmer’s GRM

Interpretations on Line 00 (or 1000N)

at Mt Bulga

Class tutorial

Prof. Bob Whiteley, Feb. 2012

References & bibliography

Harley, B. F. 1983. A geophysical case history of the Mt. Bulga Prospect: Extended Abstracts, 3rd Biennial

ASEG Conf., Brisbane, 31 Oct.-3 Nov. 1983, 110-115.

Leung, T.M., 2003, Controls of traveltime data and problems with the generalized reciprocal method:

Geophysics, 68, 1626–1632.

Palmer, D., 2006a, Refraction traveltime and amplitude corrections for very near surface

inhomogeneities. Geophysical Prospecting, 54, 589-604.

Palmer, D. 2006b , Integrating amplitudes and traveltimes with high resolution refraction methods.

SAGEEP2006, 1222-1240.

Palmer, D., 2009 Maximising the resolution of near-surface seismic refraction methods, Exploration

Geophysics, 40, 85-90.

Palmer, D. 2010 Characterizing the near surface with detailed refraction attributes in Advances in near-

surface seismology and ground penetrating radar: SEG Development Series, 15, Ch. 14, 233-250.

Palmer, D. 2012 Uncertainty in Near-Surface Refraction. Ext. Abs. 22nd ASEG Int. Geophysical

Conference, Brisbane, Australia, 26-29 Feb. 2012, 1-4.

Palmer D. 2011 Response to comments by Robert J. Whiteley. Exploration Geophysics, 42, 218-226.

Whiteley, R.J., Hawkins, L.V. & Govett, G.J.S. 1984 : The Seismic, Electrical and Electrogeochemical

Character of the Mount Bulga Orebody, NSW Australia, Soc. Explor. Geophys. SEG Expanded Abs, 3,

310, 310-314. Doi:10.1190/1.18403.

Whiteley, R. J., 2004 Shallow seismic refraction interpretation with Visual interactive ray trace (VIRT)

modelling. Exploration Geophysics, 35,116-123.

Whiteley, R. J. & Eccleston, P. J. 2006 Comparison of seismic refraction interpretation methods for

regolith mapping. Exploration Geophysics, 37,340-347.

Whiteley, R. J. 2011 Comments on Palmer, D. 2010. Is visual interactive ray trace an efficious strategy

for refraction inversion, Exploration Geophysics, 41, 260-267. Exploration Geophysics, 42, 207-217.

• Palmer (2009, p87 & p89) has stated that the GRM, a ray-based refraction

interpretation method introduced 40 years ago, is a subjective and empirical

method. It relies on supposed improved performance based on simplified seismic

models.

• The GRM contains all the model assumptions of the Reciprocal (Plus-Minus)

Method (~ 50 years old) with the additional assumption that an “optimum XY” can

be reliably extracted from processed first arrival data. In application, the GRM

requires a simplified overburden velocity model.

• The theoretical basis that an “optimum XY” actually exists in variable earth models

and meets Palmer’s definition has not been established.

• Using other more complex seismic models representing laterally variable earths

Leung (2003) has shown that extraction of an “optimum XY” using Palmer’s

criteria is unreliable.

• Interpreted seismic sections produced with the GRM in variable conditions do not

produce synthetic TX data whose times agree with measured TX data from inner

and near end shots where overburden velocities are represented. This is in

contrast with tomography i.e. how do you check GRM interpretations?

700 000

6 330 000

Modified from Agnew et. al. (2005). Lewis Ponds, a hybrid carbonate and volcanic-hosted

polymetallic massive sulphide deposit, New South Wales, Australia. Mineralium Deposita,

39, 822-844.

Mt. Bulga

Location of the Mt. Bulga Massive Sulphide Deposit

Line 00N

Palmer Stn. 49

Whiteley Stn. 100E

From Harley (1983)

Approximate location of Palmer’s

(2006) & Whiteley’s (1984) refraction

lines at Mt Bulga with local geology

Line 00N

Palmer Stn. 49

Whiteley Stn. 100E

1: DDH 9 outcropping

weathered volcanics

2:Old collapsed

workings, with

the highly porous

Mt Bulga gossan

extending to the

ground surface,

note the sharp

contact with the

volcanics. Top of

arch is at ~8m

depth.

3: Close up of

Mt Bulga gossan

showing

extensive voids

and wallrock

collapse breccia

(dime gives

approx. scale)

1984 site

photos

Looking east Mt

Bulga deposit is

at crest of ridge

Looking south

SP1

SP97

Palmer’s (2006a, Figure 2) TX data. Data from the offset shots SP1 and SP 97 were used for

the GRM interpretations but not for the various tomographic models unless Palmer created

artifical data to connect the offset shots with their respective shot points (unlikely).

The TX data from the offset shots

(white) are not used by Dr Palmer

for the tomographic models. The

far offset shot data is used for his

GRM models

SP1

SP97

Palmer’s data:

segmented, 3

or 4 layers?

SP 1

SP 97

SP 1 and SP 97 data

were used for Palmer’s

GRM interpretations

SP1

SP97

Parallelism shows that offset shot

data from SP1 and S97 are

inconsistent with critical refraction

from the same refractor. (Data from

SP13 and SP85 have been overlain).

Therefore, none of Dr Palmer’s

GRM interpretations can be correct.

Original refraction data

& Reciprocal Method

(RM) Interpretation

Whiteley et al. (1984 )

Approx. location of

overlap with

Palmer’s data

Diffractions from the

western margin of the

ore zone

Diffractions from the

eastern margin of the

ore zone

Palmer’s (2006a, Figure 17 )

various GRM interpretations

using data from SP 1 and SP 97

Palmer’s (2006b, Fig. 18)

GRM interpretation

Are any of these interpretation correct ?

How do we check and which one do we use?

Ground surface

differs due to

rehabilitation

works after

Whiteley’s survey

Comparison of Whiteley’s

(1984) RM with Palmer’s

(2006a, Fig. 17) GRM

interpretations for XY = 2.5m

Comparison of Whiteley’s

(1984) RM with Palmer’s

(2006b, Fig. 18) GRM

interpretations for XY = 2.5m

Ground surface

differs due to mine

rehabilitation works

after Whiteley’s

survey

RM AND GRM

interpretations

(Palmer 2006a, Fig.

17) with XY = 2.5m

Tomogram from

Palmer (2012, Fig. 3).

No offset data used

Initial VIRT (Whiteley, 2004)

interpretation of Palmer’s

data with raypaths from SP 1

and SP 97 by

Tak-Ming Leung (completed

in 2009)

Note close fit with inner and

near offset source data,

deepest refractor represents

approx. base of weathering

and top of the fresh

sulphides.

The fit to the offset data

could be improved a little

with some more VIRT

modelling but this would not

change things much.

MW-SW Volcanics

SW-F Volcanics

MW Volcanics

EW Volcanics

Soils & EW Volcanics

SW - F Meta seds.

MW-SW Meta seds.

EW Meta seds.

Soils

Porous Gossan

Supergene ore with

mine voids

Fractured/altered

massive sulphides

Whiteley’s Geological Interpretation of VIRT Model obtained from Palmer’s data

Significant diffraction sources

Weathering codes used:

EW - Extremely

MW – Moderately

SW – Slightly

F- Fresh

Interface in this

region not well

defined

Tomogram from

Palmer (2012, Fig. 3)

Comparison

of tomogram

with VIRT

model

Outcropping

weathered volcanics

Mt Bulga gossan

Soils & deeply

weathered

siltstones

Interface in this

region not well

defined by the

seismic data

Comparison of GRM

interpretation (Palmer

2006b, Fig. 18) with

VIRT model

Forward offset shot ray paths (dashed lines) from SP1 at -60m

A

B C D E

Relative first

arrival

amplitudes

from Palmer

(2006, Figure 9)

Forward ray

groups, note

rapidly

decreasing

amplitudes over

low velocity

gossan (Zone C)

FGHIJ

K

Reverse offset shot ray paths (solid lines) from SP97 at 180m

Reversed ray

groups, again

note rapidly

decreasing

amplitudes

over low

velocity gossan

(Zone H)

Comments:

• Dr Palmer’s GRM interpretations on Line 00 at Mt. Bulga are

inconsistent with the assumptions contained within the GRM

• Comparison between tomographic images from various GRM

starting models in Palmer (2012) is technically questionable as

the inversion process has not used the offset TX data used for

the GRM models. So what is being compared?

• First arrival amplitude behaviour is inconsistent with Palmer’s

GRM interpretations

Prof. Bob Whiteley, Feb. 2012