APPLICATION OF INDICATOR HALOS (SIGNS OF ORE REMOBILIZATION) IN EXPLORATION FOR BLIND GOLD AND SILVER DEPOSITS

The indicator method is a new, effective exploration method for blind ore. This method is based on the partial redeposition of ore and vein matter in the overlying rocks as a result of the magmatic, hydrotherma l, and tectonic processes. Studies of ''standard'' deposits with blind ore show that geochemical and mineral halos of redeposited matter fro m blind ore bodies (indicator halos) occur in post-ore geological bodi es termed ''lifts'' - faults, dikes, and quartz veins within the overl ying rock. The indicator method uses special sampling of the past-ore lift structures. The proposed technique can be used to search for blin d ore mineralization in different geological environments. The post-or e dikes are sampled across the strike of the prospective blind ore str uctures. Dike material is analyzed for Au, Ag, Sn, Pb, Zn, Cu, CO2, an d SO4. Experiments completed in the well-studied Ducat mining field su ggest that this method is applicable over a vertical range of more tha n 200 m. The ''resolution'' identifies individual blind ore bodies as well as groups of orebodies. The post-ore fault method includes sampli ng of the sand-size fraction of cataclastic material from these fault zones, extraction of the paramagnetic fraction, and semi-quantitative analysis of this fraction for the content of indicator elements. Our s tudy has shown this method to be effective in exploration for blind or e at 1 : 10 000 scale. The vertical range of this method is more than 300 m. The possibility of predicting the composition and average gold and silver grades within the blind ore is also shown. Post-ore quartz veins are sampled and rapidly checked for selected indicator elements using a portable X-ray fluorescence (XRF) instrument. The testing of t his method has identified several new orebodies. With the aim of impro ving the sampling methods, the sample preparation methods and the anal ysis of the samples for the indicator halos in the post-ore faults, st udies of the following modifications to the indicator method were carr ied out: (1) sampling of the fine (rock dust) fraction from fault zone s; (2) sampling of the sand-size fraction by the rapid XRF method; and (3) sampling of mosses in the post-ore fault zones (the bryogeochemic al method). The proposed modifications suggest that these methods can be used in a wide range of geographical landscapes.