Geophysical exploration and geological appraisal of the Siah Diq porphyry Cu–Au prospect: A recent discovery in the Chagai volcano magmatic arc, SW Pakistan

Abstract

Discovery of the Siah Diq porphyry (Cu–Au) prospect in the foothill of Dam Koh volcano is a recent exploration success story of mineralization buried under a 46 m alluvium cover in an exploratory mature Chagai belt. Acquisition of geophysical data followed by drilling and logging was key in the discovery. Integrated magnetics and induced polarization (IP) surveys in an area of 7.5 km², pointed out magnetic-low, IP-high, and resistivity-low anomalies corresponding to porphyry Cu–Au type sulfide mineralization. Three bore holes were drilled to test the geophysical anomalies. After careful observation and geoscientific logging of core, porphyry style Cu–Au mineralization was revealed. The porphyry prospect was further characterized based on host rock lithology, petrography, alteration mineralogy, ore vein characterization, and Cu/Au geochemical assays based on core samples. Rocks hosting the mineralization include andesite, granodiorite, coarse, as well as fine grained diorite and pink granite, all highly altered, mineralized and porphyritic. Propylitic alteration was dominant in all the three bore holes and developed earlier followed by phyllic, potassic, and argillic alterations. Sulfide mineralization is present as cross-cutting stockwork veins and disseminations. Average copper and gold assays of drill core are 0.17% Cu and 0.78 ppm Au, respectively. Economically insignificant values of molybdenum and silver have been noted in some samples.