Response to Reply. Article “Theory behind the use of soil pH measurements as an inexpensive guide to buried mineralization, with examples” by Barry Smee in Explore 118, Jan 2003.
Response submitted by Alan W. Mann, Perth, Western Australia, in Explore 120, July 2003.
Reply to Alan Mann:
Submitted by: Barry W. Smee, Sooke B.C., Canada
The letter from Alan Mann in EXPLORE issue 120 responds to my previous article in Explore 118 (Smee, 2003) regarding the use of soil pH and its affect on selective or weak extraction (SWE) methods. Dr. Mann takes me to task, at some length, for the first paragraph where I suggest, not too subtly, that some of the reporting of results of certain commercially sold SWE methods may not be offering a clear picture of the difficulties involved in their use. I stand by my claim, without apologies.
My accompanying note in the Explore 118 issue contained the hope that there would be replies to Explore with “sharp wits and enthusiasm”. Perhaps what I should have said is “additional useful data and insights into the Geochemical Process”, which was one of the focus topics of the issue. Alan offers neither useful data nor insights.
Some years ago I reviewed the historical development of SWE methods Smee (1997). That communication quotes several geochemists who gave warnings into the use of SWE methods alone: for example, Boyle and Smith (1968) said that “geochemistry has suffered with a poor reputation” because of the use of SWE methods by untrained personnel. Fisher (1971) in his research on SWE methods showed that the amount of metals dissolved is affected by particle size, complexes formed, mineral composition of the sample and drying time. It appears that much this work has been forgotten or ignored. If it has not, why do the SWE providers not offer methods of correcting SWE data to account for these variables?
Bradshaw et al. (1974) showed that it is complete folly to present SWE data alone without corresponding strong acid extraction data to act as a baseline. They also point out (remember this is now 29 years ago): “The depth of sampling during the soil programme may be very critical as variations with depth can be greater than a factor of ten within 6 inches.” The sampling of specific soil horizons to enhance SWE responses is not at all new news as indicated by Mann et al, 1998.
Govett and Chork (1977) showed that the use of organic analyses was important to the interpretation of SWE geochemistry in sampling mineral soils, while Nuutilainen and Peuraniemi (1977) showed that the metal-organic ratio enhanced geochemical anomalies in humus samples. These papers together clearly implicate the organic content of soil as important to the interpretation of SWE geochemistry, but is different for different soil horizons. Why are the results of commercial SWE methods as used in temperate environments not corrected for the number of organic, iron and manganese binding sites?
My 1983 paper suggested that the organic content of the soil is dependent on soil bacteria concentrations and types, which is in turn affected by soil pH. Stuart Hamilton has recently come to the same conclusion (Hamilton personal comm., 2003) from his excellent work in Ontario. Why are the commercial providers of SWE methods not performing their own research into these topics to aid their clients?
Dr. Mann chides me in not referencing the excellent research undertaken by Gwendy Hall and her team at the Geological Survey of Canada, and suggests that I have insulted her by not doing so. Firstly, Gwendy’s work is primarily focused on the analytical problems associated with SWE methods rather than geochemical processes. Secondly, I have known and worked with Gwendy for nearly thirty years: if I insulted her I would be the first to hear about it—from her! I have been assured by Ms. Hall that I did not insult her in the Explore 118 article.
Dr. Mann determines, somehow, that I am maligning the use of SWE methods. I have been using SWE methods in mineral exploration for more than thirty years, and continue to do so routinely. However I never use the SWE methods alone as a single means of defining drill targets. I do use the SWE methods along with the corrective actions that have been outlined by workers for over thirty years.
My colleagues may notice that in all of my published work on SWE methods, dating from 1972, (in: Bradshaw et al, 1969, 1970, 1971, 1972a, b) I have never used SWE analyses alone to interpret data. I have attempted to account for as many variables as I know before plotting final data. This is why I use the ratio of the SWE analysis to the hot acid analysis and to the organic carbon content or calcium and/or iron content when applicable. These interpretation methods have proven to hold true over my thirty five years in the geochemical business and have contributed to the discovery of VMS massive sulphides, shale-hosted massive sulphides and a variety of gold deposits. My work on soil pH speaks to the process of anomaly formation and more importantly, anomaly discrimination, not to the exclusion of SWE methods.
I am particularly miffed at the commercial providers of SWE methods who either ignore past work, or re-discover the wheel. The commercial providers of SWE methods are selling a product that charitably they really don’t understand. Mann quotes the Birrell and Mann 1999 presentation at the 19th IGES Workshop that showed the carbonate problem with MMI A leach and other unbuffered SWE methods. I illustrated the same problem in Explore 102. Why did it take the MMI providers at least 3 years of commercial sales to discover this relatively simple problem? Did they reanalyze their client’s MMI A affected samples with MMI C? What other surprises wait in the wings for the commercial SWE users?
If exploration geochemistry is to understand the complex processes and interactions of ion migration then there cannot be secrets in methods. It is time to open the “black boxes” and get on with discoveries.
Boyle, R.W. and Smith, A.Y., 1968: The evolution of techniques and concepts in geochemical prospecting. In The Earth Sciences in Canada (ed. E.R.W. Neale), Royal Soc. Canada Spec. Public. No. 11, 117-128.
Bradshaw, P.M.D., Clews, R.D., Walker, J.L., 1969-1972: Exploration Geochemistry. Mining in Canada, Dec.1969, Feb. 1970, April 1970, June, 1970, Canadian Mining Journal, Aug. 1971, Dec. 1971, May 1972.and continental glaciation. Prospectors and Developers Association of Canada, Annual Number.
Bradshaw, P.M.D., Thomson, I., Smee, B.W. and Larsson, J.D., 1974: The application of different analytical extractions and soil profile sampling in exploration geochemistry. J. Geochem. Explor., 3: 209-225.
Fisher, N.H., 1971: Recent research in geochemical prospecting in Australia In Geochemical Exploration, CIMM Spec Vol.. 11, 16-20.
Govett, G.J.S. and Chork, C.Y., 1977: Detection of deeply buried and blind sulphide deposits by measurement of organic carbon, hydrogen ion and conductance in surface soils. In: Prospecting in Areas of Glaciated Terrain, IMM Publ. pp.49-55.
Mann, A.W., Birrwll, R.D., Mann, A.T., Humphreys, D.B., and Perdrix, J.L., 1998: Application of the mobile metal ion technique to routine geochemical exploration. J. Geochem. Explor. 61: 87-102.
Nuutilainen, J. and Peuraniemi, V., 1977: Application of humus analysis to geochemical prospecting: some case histories. In: Prospecting in Areas of Glaciated Terrain, 1977. IMM Publ., pp. 1-5.
Smee, B.W., 1983. Laboratory and field evidence in support of the electrogeochemically enhanced migration of ions through glaciolacustrine sediment. In: G.R. Parslow (Editor), Geochemical Exploration 1982. J. Geochem. Explor., 19: 277-304.
Smee, B.W., 1997: Selective extraction techniques at present and in the future. In: A workshop on exploration geochemistry in areas of present and past tropical and sub-tropical climates. Queen’s University, Kingston Ontario.
Smee, B.W., 1999: The effect of soil composition on weak leach solution pH: a potential exploration tool in arid environments. Explore 102, 4-7.
Smee, B.W., 2003: Theory behind the use of soil pH measurements as an inexpensive guide to buried mineralization, with examples. Explore, 118.
Explore, 121, p. 4-5.