UBC Theses and Dissertations
A geostatical evaluation of the southern tail zone of Equity Silver Mines, Limited, Houston, B.C. Giroux, Gary Henri
The Southern Tail zone of Equity Silver Mines, Sam Goosly silver-copper deposit presents an interesting challenge not only for global and local ore reserve estimations, but also for maintaining quality control on sampling and assaying. Silver grades from both stockwork and massive galena-sphalerite lenses vary as much as, 3 orders of magnitude across very short distances. Geostatistical methods have been developed to minimize the effects of erratic mineralization on reserve estimation and quality control. Conditional probability is demonstrated as a global ore reserves estimation method for the Southern Tail zone using exploration diamond drill data. The entire procedure, including declustering, structural analysis and conditioning raw data distributions to block grade distributions is outlined. Results are presented as a grade tonnage curve and compared to estimates calculated by inverse distance. A statistical and graphical approach to evaluating paired data is presented as a method of monitoring the quality of sampling and assaying. Results from the Southern Tail zone indicate a bias in silver analyses between two laboratories, a large random error in the standard tube sampling technique for blasthole cuttings and an inverse relationship between sampling error and sample volume. An idealized calculation based on possible improvement of sampling method indicates that a significant increase in metal recovery could be attained through better sampling. For local block estimation, a variety of kriging techniques have been evaluated and compared with inverse distance and polygonal estimates. Both cross validation and comparison of kriging errors showed that log kriging of selection mining units using partitioned sample data is superior to other methods, although only marginally so in some cases. For a test area of 100 blocks on the 1310 N bench estimated by the various methods, the polygonal method predicted 1.4 million grams of silver more than a log partitioned method. While no conclusions can be drawn as to which method is correct, the necessity of monitering the metal content from specific blocks early in the production life of a mine is stressed.
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