The geology and mineralization of the Sar-e-Yazd Cu (Mo) Porphyry Deposit in the Saveh-Naein-Jiroft magmatic belt (SNJMB), Iran

Abstract

The Sar-e-Yazd Cu (Mo) deposit is located in the Naein-Jiroft magmatic belt or Kerman belt. It is in the southern part of the Cenozoic Saveh-Nain-Jiroft magmatic belt of Iran. This deposit is spatially associated with Oligocene shallow porphyritic porphyries intruded into dacite porphyry to porphyritic quartzdiorite and middle Eocene volcanoclastic rocks. Hypogene ore minerals include chalcopyrite, magnetite, pyrrhotite, molybdenite, bornite and pyrite occurring as veinlets and disseminations mostly in the both intrusive rocks. Hydrothermal alteration from inside to outside is marked by potassic, carbonate alteration, an extensive phyllic assemblage and irregular zones of propylitic (actinolite, epidote and chlorite sub-zone) and clay assemblages with no consistent zoning patterns. The study of faults in the area reveals that, in general, they align with the pre-existing joints in the structure of the Sani Abad syncline. These faults are attributed to ancient fractures within the right-lateral shear system between the Anar and Dehshir right-striking faults. Three sets of faults are recognized in the eastern Mehriz area (Sar-e-Yazd region): 1– longitudinal direction joints (or tension faults), along with early intrusions and the first group of dykes with WNW–ESE extension, are attributed to old T2 fractures in the shear system. However, the second group of later dykes, often intruded in a N–S direction, is attributed to tensile fractures in the T1 shear system, 2 – cross direction joints (or expansion faults) and 3 – diagonal direction joints (or shear faults; the late intrusive, branches of the epithermal Cu-Fe and the Pb-Zn apophyse intruding aligned with these faults direction. The veins shows two main trends: a- tension split is related to T1 and tensile fractures (epithermal Cu-Fe veins) and b- the pennant vein pattern is related to R/R’ diagonal fractures. Fractures with the NW–SE trend (R), which are mostly filled by iron oxides, are younger and don’t have an effective role in mineralization and it seems that the fractures with the R’ shear system have been effective in the placement of intrusive. The total average of the highest metallic mineralization is enriched in supergene zone at each boreholes (BH): BH01, BH03, BH04 and BH23. Cu: 3881 ppm, Mo: 43.7 ppm, Pb: 13390 ppm, Zn: 18250 ppm and Ag: 6.7 ppm in the 25 to 58 m depth. Fluid inclusion studies indicate a wide range of homogenization temperatures in the veinlets and phyllic porphyritic quartzdiorite alteration, ranging from 136°C to 542°C, with salinities of 4–62 wt.% NaCl equivalent. The coexistence of vapour-rich inclusions (F3 type) with high salinity and liquid-rich inclusions (F2 type) with similar Th values provides strong evidence for boiling. Parts of the copper content in the solution could be deposited as a result of boiling processes as chalcopyrite which was the major mineral at the Sar-e-Yazd deposit (similar to porphyry copper deposits). The analysis of borehole samples indicates a moderate correlation between Cu and Mo, suggesting porphyry Cu (Mo) deposits in Sar-e-Yazd. Cu also shows a strong correlation with Pb, Zn, and Ag, which are key indicator elements of these deposits. Finally based on the distribution and zoning of the main metal ores, the porphyry mineralization of Sar-e-Yazd shows a significant resemblance to the Cu-Mo mineralization in the Mineral Park deposit in Arizona.