Relationship between Copper Contents in Soil and Copper Grade of Ore Bodies Calculated by Drill Core Assay of Some Porphyry Copper Deposits Tropical Terrain

Abstract

Before conducting information and outline drilling on a porphyry copper deposit, it is most advisable that the grade of copper of the target may be previously estimated by detailed geochemical study on soil sampling. To illustrate how this estimation may be carried out, geochemical data and copper contents of three porphyry copper deposits in tropical terrain, St. Niño (Philippines), Nungkok (Malaysia) and Chaucha (Equador), are compared.
1) St. Niño: The topography is very steep with very thin overburden. There are distinct dry and wet season. The average of T-Cu, Cx-Cu, Cx-Cu/T-Cu and copper content of drill cores in ore zone are 3, 048 ppm, 16.8 ppm, 0.55 percent and 0.477 percent respectively. Thus the copper content in ore body is 1.6 times the T-Cu in the soil.
2) Nungkok: The topography is also very steep. There are heavy rains all the year round in this area. The average of T-Cu, Cx-Cu, Cx-Cu/T-Cu and copper content of drill cores in the northern and southern ore zones are 2, 031 ppm, 181 ppm, 14 percent, and 0.344 percent respectively. Thus the copper content of the ore zone is 1.7 times the T-Cu in the soil.
3) Chaucha: The deposit is located about 1, 700 m above the sea level and the climate is relatively warm. The dry season starts at the middle of May and ends at the middle of October. The total rain fall in the wet season is around 1, 300 mm. The deposit is covered by the very thick overburden. The geochemical data and their relation to the drill core assay are as follows:
Therefore, the ratio of Cx-Cu/T-Cu may be one of the important factors affecting the calculation of ore grade, and this ratio may be influenced by thickness of overburden. According to the ratio of Cx-Cu/T-Cu, the copper content of ore boby will be from 1.5 to 3 times the total copper value in the soil above the ore body.