Recommendations for Generalizing the Results of Geophysical Work at Gold Ore Deposits in Transbaikalia
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This paper discusses how to periodically synthesize and reinterpret geophysical survey results from gold ore fields in Transbaikalia, using work conducted in 1960 to 1965 on the Darasun and Balei-Taseevo deposits as its basis. It outlines a methodology involving review of archival and field materials, reassessment of data quality, supplementation of petrophysical information, limited experimental-methodological studies, anomaly verification, and updated qualitative and quantitative interpretation. The authors argue that such synthesis is economically efficient, can reduce ineffective field methods and unnecessary anomaly testing, and can reveal previously unused geological information for poorly studied ore-field areas. They conclude that geophysical methods usually delineate prospective zones and structures rather than individual ore bodies, with sulfide-related methods most important at Darasun and structural geophysical methods dominant for Balei-type deposits.
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RECOMMENDATIONS FOR SUMMARIZING THE RESULTS OF GEOPHYSICAL WORK AT GOLD ORE DEPOSITS IN TRANSBAIKALIA
L. A. ZASHCHINSKII, I. P. NOVIKOV (TPI)
The need for periodic summarization of the results of geophysical work on the ore fields of gold ore deposits is due to the rapid development of methods of exploration geophysics: the creation of new techniques, improvement of their technology and instrumentation, the development of new methods of interpretation, and even the emergence of fundamentally new methods. Under these conditions, new geological information may be extracted from the results of earlier investigations, and the methodology of further work may be significantly improved. In addition, the acquisition over time of new data from geological exploration often makes it possible to radically revise previous conclusions drawn from the results of geophysical investigations and, in turn, to supplement and refine our understanding of the geological structure of a given deposit on the basis of these data.
In 1960–1965, the Department of Geophysical Methods of Prospecting and Exploration of Mineral Deposits of the Tomsk Polytechnic Institute summarized the results of geophysical work on the ore fields of two of the largest gold ore deposits in Transbaikalia: the Darasun and the Balei-Taseevo deposits.
In addition to specific geological conclusions, the results of these works provide grounds for certain general recommendations concerning the conduct of summarization: the content of these investigations, the methodology for carrying them out, their economic efficiency, and their characteristic results.
These conclusions amount to the following:
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The content of summarization work consists in a thorough analysis of the results of previously conducted geophysical investigations and their reinterpretation on the basis of the current theory of geophysical methods, taking into account the latest geological data.
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The methodology of these works includes: the study of all archival materials relating to the content of the investigations being summarized; examination of the primary field documentation in order to make an objective assessment of the quality of the work; supplementation of missing data on the physical properties of the rocks and ores composing the deposits; the carrying out, on a small scale, of experimental-methodological investigations making it possible to clarify the geological potential of methods and techniques that had been used little or not at all; systematization of the results of verification of geophysical anomalies and, most importantly, the application of the most advanced meth—
of qualitative and quantitative interpretation of the most important and characteristic anomalies.
In the course of this work, the quality of previous investigations is assessed; earlier summary documents are analyzed and qualitatively new resulting documents are compiled; general and specific conclusions are drawn about the type of deposit from the geophysical point of view, about the value of the geological information obtained as a result of conducting geophysical work, about the structure of the ore field and the prospects for ore content in its poorly studied parts, about the direction and methodology for carrying out verification of geophysical anomalies, and about ways of further applying exploration geophysics.
At the final stage of the work, a summary report on the results of the synthesis is compiled.
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The cost of the work, according to the experience of the Tomsk Polytechnic Institute, is 130–165 rubles per 1 sq. km covered by surveying in one modification at a scale of 1:5000–1:25000. These costs amount to about 10–20% of the cost of field geophysical work. Such economic efficiency should be considered very high, even without taking into account the savings obtained by abandoning the verification of obviously unpromising anomalies.
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As a result of synthesis, it is usually possible to prevent the further use of low-efficiency geophysical methods, to exclude further verification of anomalies with little promise, and to bring into use, in prospecting and exploration, previously unused geological information on the structure of poorly studied areas of ore fields.
The results of our work indicate that in most cases geophysical methods do not make it possible to localize individual ore bodies narrowly; however, they do make it possible to identify, for the targeted conduct of large-scale prospecting, areas and individual structures where the discovery of ore mineralization is most probable. An indication of the promising ore potential of an area is usually not individual anomalies, but the presence of complex anomalous patterns.
We have established that, whereas for Darasun the application of geophysical methods whose anomalies are caused directly by sulfide mineralization is of greatest importance, for the Balei type, even in very large-scale surveys (1:10000 and larger), the principal role is played by methods of structural geophysics (gravity prospecting at a scale of 1:10000, vertical electrical sounding, high-precision magnetic surveying, and seismic prospecting).