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Here is the third and last part:
Part 2: Diamond exploration in glaciated terrain
Introduction
R.N.W. DiLabio
Diamond exploration in Canada has been hampered by the lack of exploration methods that are directly applicable in glaciated terrain. Most methods that rely on the search for indicator minerals or the geochemical signature of kimberlite were developed in nonglaciated regions of the world. They can be ineffective or misleading when applied to glaciated regions, where the provenance of surficial sediments is controlled by glacial dispersal, which complicates sampling design and interpretation. Although there are many research papers on exploration for gold and base metals using glacial drift as the sampling medium (e.g., Coker and DiLabio, 1989; DiLabio and Coker, 1989), until recently, only a few papers had been published that are pertinent to the search for diamonds in Canada (Brummer et a1., 1992a,b). Attempts at the end of the last century to find the source of the mid-continent diamonds found in glacial drift recognized the complications involved and invoked glacial transport to explain the distribution of diamond discoveries (Hobbs, 1899). Much later, Lee (1965, 1968) showed that pyrope recovered from esker sediments near Kirkland Lake, Ontario could be traced up-ice to kimberlite bedrock. Recently, the Kirkland Lake area again became the focus for studies aimed at developing and refining exploration methods (McClenaghan, 1996). In new areas where diamond exploration has been active, research into drift prospecting methods continues (Ward et a1., 1996; Garrett and Thorleifson, 1996), and biogeochemical exploration methods for finding kimberlite have been tested at several sites (Dunn and McClenaghan, 1996).
The single most important feature of glaciated terrain that complicates exploration using drift mineralogy or geochemistry is the exotic provenance of glacial drift. Bedrock is glacially eroded and dispersed away from its source along glacial bowlines, which can trend up regional slopes, cross drainage divides, shift through the course of a glacial cycle, and deviate markedly from post-glacial drainage patterns. For example, Veillette and McClenaghan (1995) have shown that ice flow during the last glaciation in the Abitibi-Temiskaming region of Ontario and Quebec, which contains several kimberlite's, was opposite to the present flow patterns of rivers in the region. In addition, the paths followed by the ice shifted through 180 degrees during the glaciation. Therefore, it is essential to know the history of ice flow in any region under exploration, so that a mapped pattern of the distribution of indicator minerals can be traced up-ice to its source in the bedrock.
A generalized map of ice flow features from the last glaciation is shown in Figure 1. It is not meant to define the ice flow sequence at a detailed scale; shifts in ice flow cannot be displayed at the scale of this figure. Detailed mapping of glacial flow sequences is now available for many parts of Canada, particularly those areas where diamonds (and other commodities) may be found (Veillette and McClenaghan 1995; Ward et al., 1994).
References
Brummer, J.J., MacFayden D.A., and Pegg, C.C.
1992a: Discovery of kimberlites in the Kirkland Lake area, northeaster Ontario,
Part 1: Early surveys and surficial geology;
Exploration and Mining Geology, v. 1, p. 339-350.
1992b: Discovery of kimberlites in the Kirkland Lake area, northeastern Ontario,
Part 11: Kimberlite discoveries, sampling, diamond content, ages and emplacement;
Exploration and Mining Geology, v. 1. p. 351-370.
Coker, W.B. and DiLabio, R.N.W.
1989: Geochemical exploration in glaciated terrain - geochemical responses,
at Exploration '87, G.D. Garland (ed.);
Ontario Geological Survey, Special Volume 3, p. 336-383.
DiLabio, R.N.W. and Coker, W.B.
1989: Drift Prospecting;
Geological Survey of Canada; Paper 89-20, 169p.
Dunn, C.E. and McClenaghan, M.B.
1996: Biogeochemical studies of kimberlites;
Searching for Diamonds in Canada,
A.N. Lecheminant, D.G. Richardson, R.N.W. DiLabio and K.A. Richardson (ed.);
Geological Survey of Canada. Open File 3228, p. 219-223.
Fulton, R.J.
1995: Surficial materials of Canada;
Geological Survey of Canada, Map 1880A.
Garret: R.G. and Thorleifson, L.H.
1996: Kimberlite indicator mineral and soil geochemical reconnaissance of the Canadian Prairie region,
Searching for Diamonds in Canada,
A.N. Lzclheminant, D.G. Richardson, R.N.W. DiLabio, and K.A. Richardson (ed.);
Geological Survey of Canada, Open File 3228, p. 205-211.
Hobbs, W.H.
1899: The diamond field of the Great lakes;
Journal of Geology, v. 7, p. 375-388.
Lee H.A.
1965: (1) Investigation of eskers for mineral exploration, (2) Buried valleys near Kirkland Lake , Ontario;
Geological Survey of Canada, Paper 65-14, 20p.
1968: An Ontario kimberlite occurrence discovered by application of the glaciofocus method to a study of the Muluo esker;
Geological Survey of Canada, Paper 68-7, 3p.
McClenaghan, M.B.
1996: Geochemistry and indicator mineralogy of drift over kimberlite, Kirkland Lake, Ontario;
Searching for Diamonds in Canada,
A.N. LeCheminant, D.G. Richardson, R.N.W. DiLabio, and K.A. Richardson (ed.);
Geological Survey of Canada, Open File 3228, p. 213-218.
Veillette, J.J. and McClenaghan, M.B.
1995: Sequence of ice flow in the Abitibi-Temiskaming region; implications for mineral exploration and dispersal of carbonate, Quebec and Ontario;
Geological Survey of Canada, Open File 3033.
Ward, B.G Dredge L.A., and Kerr, D.E.
1994: Ice flow indicators, Winter Lake (86 A), Lac de Gras (76 D), and Aylmer Lake (76 C), District of MacKenzie, N.W.T.;
Geological Survey of Canada, Open File 2808.
Ward, B.C., Dredge, L.A., and Kerr, D.E., and Kjarsgaard, I.M.
1996: Kimberlite indicator minerals in glacial deposits, Lac de Gras areas N.W.T.;
Searching for Diamonds in Canada; A.N. LeCheminant, D.G. Richardson. R.N.W. DiLabio, and K.A. Richardson (ed.);
Geological Survey of Canada, Open File 3228, p. 191-195.
Part 3: Geophysical exploration and Geographic Information System (GIS) applications
Introduction
K. A. Richardson
The published record of using geophysics in the search for diamonds goes back 65 years to Stern's (1930) report on a geomagnetic survey to locate diamond- bearing intrusions in Arkansas, U.S.A. Although ground and airborne magnetic surveying continue to play a fundamental role in diamond exploration, many other geophpical methods are now being used to define broad prospective terraces, and to detect and delineate diamond-bearing bodies.
Magnetic surveys were used extensively in Yakutia, Russia in the 1950s and 1960s (Atkinson, 1989) and the use of aeromagnetic surveying, in conjunction with colour air photography in prospecting for "diamond deposits in situ" on the Siberian platform was reported by Barygin (1962).
Other geophysical methods included in Gerryts (1970) review of geophysical practice in diamond prospecting worldwide are gravity surveys (USSR and Africa), and resistivity surveys (Africa), in addition to magnetometer surveys (USA, USSR, and Africa). Gerryts concluded that gravity and resistivity methods were useful only on a local scale, and magnetics offered the only airborne method that produced positive results.
In 1970, Burley and Greenwood (1972) carried out a number of geophysical investigations (magnetic, resistivity, gravity, electromagnetic and seismic) to determine the most suitable exploration methods for diamond bearing kimberlite in Lesotho, Africa. They found that magnetic and resistivity methods were most useful for ground follow-up; gravity and electromagnetism could be useful in defining weathered kimberlites; gravity surveys produced small anomalies that could be used to locate buried pipes; and seismic refraction was unlikely to detect buried kimberlites within the basalt of the study area.
By the end of the 1970s, when Macnae (1979) reviewed geophysical techniques for kimberlite prospecting, airborne electromagnetics (AEM) had proved effective to detect pipes in South Africa. He presented several examples from ground magnetic and resistivity surveys, and airborne EM and magnetic surveys, over two areas in South Africa, and concluded that AEM is a particularly important complement to aeromagnetics in areas of deep weathering. Smith (1985) discussed the use of ground and airborne EM at Ellendale, Western Australia, where AEM responses upgraded very weak magnetic responses.
A decade later, Atkinson (1989) reviewed the state of diamond exploration, and although many ground geophysical techniques had proved effective to delineate the boundaries of kimberlite pipes, aeromagnetic surveys still provided the only rapid, inexpensive reconnaissance exploration tool. The combination of radiometrics with magnetics, however, was the most widely used airborne geophysical method of diamond exploration in Australia.
There is little published on the results of radioactivity survey applied to diamond exploration. Macnae (1979) referred to work by Paterson et at. (1977) that found ground radiometric techniques to be of limited use in Lesotho, but anomalies were too small for airborne reconnaissance detection. Although Drew (1986) described an aeromagnetic/radiometric survey of the area of the AK1 lamproite pipe in Western Australia, in which the radiometric data failed to locate a recognizable response over the pipe, Jenke and Cowan (1994) described a successful application of airborne radiometrics in mapping black soil cover in the Ellendale lamproite province, where a number of diatremes were detected. Small airborne gamma-ray spectrometer surveys were flown by the Geological Survey of Canada in the Sturgeon Lake area, Saskatchewan (Hetu, 1989) and at Lac de Gras, Northwest Territories (Shivas and Holman,1995). Neither of these test surveys produced detectable gamma radiation responses from known kimberlites, but the gamma ray results, with accompanying magnetometer and VLF-EM data, did provide useful information on the bedrock and surficial geology. Macnae (1995) provided a recent and comprehensive review of the role of exploration geophysics in locating primary diamond deposits, with emphasis on integrated airborne EM and magnetic surveys. He referred to reports of anomalous radioactive responses for kimberlites in India and Siberia, and also gave an example of a seismic reflection profile over a Yakutian kimberlite.
Brummer's (1978) review, "Diamonds in Canada", mentioned the use of regional geophysical anomalies as broad indicators of areas favourable for kimberlite occurrences, but diamond exploration in Canada up to that time was based largely on glacial drift and stream sediment sampling for indicator minerals, rather than on geophysical surveying.
When a later version of his paper was published (Brummer, 1984) high-resolution airborne magnetic and electromagnetic methods were increasingly applied to the search for diamonds in Canada, and the "Great Canadian Diamond Rush" of the 1990s, has seen extensive use of these airborne geophysical techniques, as well as ground geophysical methods for follow-up and location of drill targets.
The following 8 papers in this volume outline work by the Geological Survey of Canada involving geophysics and petrophysics, remote sensing, and the application of geographic information system in searching for diamonds in Canada. Keating et at. (1996), presented the status of the National Aeromagnetic Data Base. Systematic aeromagnetic survey data, acquired since 1947, cover much of Canada, and provide a database that continues to be instrumental in the discovery of kimberlite fields. They also illustrated the extensive gravity coverage that can contribute on a regional scale to assess the potential of an area for diamond genesis and preservation (Morgan 1995). In a second paper, Keating (1996) presented an automated technique for identifying aeromagnetic anomalies that could be caused by kimberlite pipes, and showed how the combination of AEM data with magnetic data improves the technique.
Danube and Kjarsgaard (1996) and Mwenifumbo et al. (1996) discussed physical property measurements of kimberlites, as measured in the petrophysics laboratory and in situ using borehole geophysical methods. The laboratory data show differences between hypabyssal, diatreme, and crater facies kimberlites. Borehole measurements of electrical conductivity and gamma radioactivity at Fort a la Corne enabled classification of kimberlite in one drill hole into five phases or separate eruptions.
Morgan (1995) discussed an exploration strategy based on the search for lithospheric conditions favourable to diamond genesis and preservation. Key characteristics for target areas are low surface heat flow over 300 to 400 km diameter regions, lithospheric thickness of >150 km, relatively deep lithospheric electrical conductors, slow seismic velocities, and great depths to the seismic low velocity zone. Jones et al. (1996) gave an overview of experiments from Canada's LITHOPROBE program (i.e., a new generation of teleseismic and deep-probing EM techniques), which contribute to the study of the continental lithosphere, and provide information about the age, thickness, and internal geometry of the upper mantle that optimizes strategies for regional kimberlite exploration.
On a more local scale, Gendzwill and Matieshin (1996) completed a reflection seismic investigation over a known kimberlite body at Fort a la Corne, Saskatchewan, as a test to define the geometry and structure of the body. Whereas refraction seismic has been used to map the edges of a kimberlite in South Africa (da Costa, 1989), only recently have applications of seismic surveying to kimberlite mapping (Erkhov et al., 1993) been reported ( Macnae, 1995). Gendzwill and Matieshin's work on a Fort a la Corne area kimberlite amplified the geological interpretation from drilling data, and indicated the shape, extent, and stratigraphic relationship of the body.
Rencz et al. (1996) presented an interesting application of thermal imagery from LANDSAT to locate kimberlite pipes.
Lakes in the vicinity of Lac de Gras that have lower water temperatures relative to other lakes of similar size were identified from the satellite imagery. The lower temperatures indicate greater water depths, and this is attributed to deep glacial excavation of easily eroded kimberlites.
In addition to the variety of geophysical measurements from airborne and ground surveys, the database that is used in a diamond exploration program may include bedrock and surficial geological observations, geochemical survey data, and remotely sensed airborne and satellite imagery. The management, integration, analysis and interpretation of such a complex array of information, obtained from different sources and in different forms, presents a challenge to the user. In the final paper of this volume, Bowie et al. (1996) describe one technique, a Geographic Information System, that provides an efficient means of handling multidisciplinary data. The use of this technology in the Lac de Gras region demonstrates how GIS provides new ways to process large arrays of information, and how it might be applied in the search for diamonds.
References
Atkinson, W.J.,
1989: Diamond exploration philosophy, practice, and promises: a review,
Proceedings of the Fourth International Kimberlite Conference, Kimberlites and Related Rocks:
Their Mantle/crust Setting, Diamonds and Diamond Exploration, J. Ross (ed.), v. 2.,
Geological Society of Australia, Special Publications no.14, p. 1075-1107.
Barygin, V. M.
1962: Prospecting for kimberlite pipes from the air;
The Mining Magazine, London, v. 107, p. 73-78.
Bowie, C., Kjarsgaard BA., Broome H.J., and Rencz, A.N.
1996: GIS activities related to diamond research and exploration, Lac de Gras areas, District of Mackenzie, N.W.T.;
Searching for Diamonds in Canada,
A.N. LeCheminant, D.G. Richardson, R.N.W. DiLabio and K.A. Richardson (ed.);
Geological Survey of Canada, Open File 3228, p. 259-263.
Brummer, J.J.
1978: Diamonds in Canada;
Canadian Mining and Metallurgical Bulletin, v. 71, no. 798, p. 64-79.
1984: Diamonds in Canada;
The geology of industrial minerals in Canada, Canadian Institute of Mining and Metallurgy,
Special Volume 29, G.R.Guile & WMartin, (eds.), p. 311-320
Burley, A.J. and Greenwood, P.G.
1972: Geophysical surveys over kimberlite pipes in Lesotho;
Institute of Geological Sciences, Geophysical Division,
Report No. IGS 540 100 9/72, 32 p.
da Costa A.
1989: Palmietfontein kimberlite pipe, South Africa - a case history;
Geophysics, v. 54, p. 689-700.
Drew, G.J.
1986: A geophysical case history of the AK1 lamproite pipe (extended abstract);
Fourth International Kimberlite Conference, Geological Society of Australia
Abstract Series Number 16, Perth, Western Australia. p. 454-456.
Erkhov, V., Erinchek, Y., Dobrynina N., Grib, V., Yefimov, A., Kalinin, 0., Kontaovich, R., Parasotka, B., and Cherny, S.
1993: Geophysics of sub-vertical objects: advanced prospecting technology for kimberlite pipes;
Society of Economic Geologists/Moscow :93, Abstracts.
Gendzwill, D. and Matieshin, S.
1966: Seismic reflection survey of a kimberlite intrusion in the Fort a la Come district, Saskatchewan;
Searching for Diamonds in Canada,
A.N. LeCheminant, D.G. Richardson, R.N.W. DiLabio and KA. Richardson (ed.);
Geological Survey of Canada, Open File 3228, p. 251-253.
Gerryts, E.
1970: Diamond prospecting by geophysical methods - a review of current practice;
Mining and Groundwater Geophysics/1967, L.W. Morley (e,d.),
Geological Survey of Canada Economic Geology Report No. 26, p. 439-446.
Hetu R
1989: Saskatchewan Kimberlite Study: Airborne Gamma-ray Spectrometric Test Survey;
Geological Survey of Canada Open File No. 2128.
Jenke, G. and Cowan, D.R.
1994: Geophysical signature of the Ellendale lamproite pipes, Western Australia;
Geophysical Signatures of Western Australian Mineral Deposits,
University of Western Australia. Perth. p. 403-414.
Jones, , A.G. Eaton, D., White, D., Bostock, M., Mareschal, M., and Cassidy, J.
1996: Passive geophysical measurements for lithospheric parameters;
Searching for Diamonds in Canada
A.N. LeCheminant, D.G. Richardson, R.N.W. DiLabio and K.A. Richardson (ed.);
Geological Survey of Canada, Open File 3228, p. 243-250.
Katsube, T.J., and Kjarsgaard, B.A.
1996: Physical characteristics of Canadian kimberlites;
Searching for Diamonds in Canada,
A.N. LeCheminant, D.G. Richardson, R.N.W. DiLabio and KA. Richardson (ed.);
Geological Survey of Canada Open File 3228, p. 241-242.
Kiting, P.
1996: Kimberlite and aeromagnetics;
Searching for Diamonds in Canada,
A.N. LeCheminant, D.G. Richardson, R.N.W. DiLabio and KA. Richardson (ed.);
Geological Survey of Canada, Open File 3228, p. 233-236.
Keating, P., Tod, J., and Demon: R.
1996: The national antimagnetic database;
Searching for Diamonds in Canada
A.N. LeCheminant , D.G. Richardson, R.N.W. DiLabio and KA. Richardson (ed.);
Geological Survey of Canada Open File 3228, p. 229-232.
Macnae, J.
1979: Kimberlites and exploration geophysics;
Geophysics, v. 44, no. 8, p. 1395-1416.
1995: Applications of geophysics for the detection and exploration of kimberlites and lamproites;
in Diamond Exploration into the 21st Century, W.L.Griffin (ed.),
Joumal of Geochemical Exploration. v. 53, p. 213-243.
Morgan, P.
1995: Diamond explortation from the bottom up: regional geophysical signatures of lithosphere conditions favorable for diamond exploration;
Diamond Exploration into the 21st Century, W.L.Griffn (ed.),
Journal of GeochemicalExploration, v. 53, p. 145-165.
Mwenifumbo, CJ., Hunter, J.A.M., and Killeen,P.G.
1996: Geophysical characteristics of kimberlites;
Searching for Diamonds in Canada,
A.N. LeCheminant, D.G. Richardson, R.N.W. DiLabio and KA. Richardson (ed.);
Geological Survey of Canada, Open File 3228, p. 237-240.
Paterson, NR., MacFadyen, D.A., and Turkeli, A.
1977: Geophysical exploration for kimberlites with special reference to Lesotho;
Geophysics, v. 42, no.7, p.1531.
Rencz, A., Bowie, C., and Ward, B.
1996: Applications of thermal imagery from LANDSAT data to locate kimberlites, Lac de Gras area, District of Mackenzie, N.W.T.;
Searching for Diamonds in Canada,
A.N. LeCheminant, D.G. Richardson, R.N.W. DiLabio and K.A. Richardson (ed.);
Geological Survey of Canada, Open File 3228, p. 255-257.
Shives, R.B.K.and Holman, P.B.
1995: Digital data for an airborne gamma ray-spectrometric, magnetic, VLF-EM survey, Paul Lake, Northwest Territories (parts of NTS 76D/9,10);
Geological Survey of Canada Open File No. 3123.
Smith, R. J.
1985: Geophysics in Australian mineral exploration;
Geophysics, v.50, no. 12, p.2637 - 2665
Stearn, N. H.
1930: Practical geomagnetic exploration with the Hotchkiss Superdip.
American Institute of Mining and Metallurgical Engmeers,Technical Publication No. 370, 31p.
nrcan.gc.ca
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