A Geostatistical Analysis Of Gold Mineralisation In Oakley’S Reef, Hutti Gold Mines, Karnataka, India

A geostatistical analysis of gold mineralisation process. characterised by discrete regular<br>samples drawn in respect of Oakley’s reef of Hutti gold fields and based on a segment of the<br>lode comprising level 10 (305 m in depth) to level 20 (620 m in depth) is presented. As the<br>stationary phenomena was observed to hold good for each level (local stationarity) but not for<br>the segment of the reef as a whole (global stationarity), geostatistical modeling was carried out<br>by processing each level data separately. In addition, the data of two vertical profiles were also<br>analysed geostatistically for a study of depth-wise variation and possible continuity of<br>mineralisation etc.<br>Variographic analysis revealed that the experimental variograms for each of the levels and<br>two vertical profiles could be represented by spherical model. However, the values for the<br>parameters C, (nugget effect), C (Sill) and a (range) of the model varied significantly from level<br>to level. High values were observed for the 16th level which is at a depth of 5 10 m. Using the<br>model parameters for each of these levels, kriging for 324 blocks of ore, each of size 30m x<br>width between one level and another, was carried out. A sample set of kriged estimates<br>together with kriged standard errors is presented. On the basis of variographic analysis it has<br>been inferred that the sample size can be reduced to half the present size without loss of<br>accuracy in the estimates for grade. This would result in substantial savings to the industry.<br>In order to quantify the chances of continuity of the mineralisation beyond the known<br>workings, Maximum Entropy Method (MEM) of spectral analysis and Markovian models were<br>found to be highly rewarding. MEM spectrum analysis revealed significant spectral spikes in<br>some of the deeper levels indicating periodicities in mineralisation ranging from<br>approximately 40 td 100 m in distance,, , and at approximately 50 m along the vertical profiles. In<br>respect of block data the estimated periodicity is from 130 to 230m along the strike and 100 to<br>300 m along the vertical profiles. Since the discrete gold assay values followed a Markovian<br>sequence, Markovian model analysis was carried out to quantify the extent(s) upto which<br>the present mineralisation pattern is likely to persist in the immediate unexplored area under<br>the assumption that the same geological conditions hold good in this area also. The likely<br>extents of gold mineralisation together with the respective probabilities of occurrence of grade ><br>2 .5 gms and > 3gms are presented.