Metallogenesis, Metallogenic Laws And Metallogenic Prediction Of The Yinan Gold Deposit, Shandong Province

As a typical skarn deposit in the western Shandong Provinc, the Yinan gold deposit is located on the west side of the Yishu fault zone (the middle segment of the Tanlu fault zone) at the southeastern margin of the North China plate. It includes the Tongjing and Jinchang ore districts which are 6 km away from each other. In the recent years, the shortage of succeeding resources is becoming a serious problem in the mine, and thus the guidance of basic theories and the systematic study on the metallogenetic laws are urgently needed. Based on comprehensive field investingations and synthetic studies on metallogenesis and ore-controlling factors by applying multiple disciplines and methods such as tectonic geology, petrology, geochemistry, fluid inclusions, isotope geology and metallogenic prediction, the metallogenic laws of the deposit are summarized in this paper. Through project attestation, good effects on ore exploration were obtained from two new prospecting targets delimited during this study.The deposit occurs at the contact zone between the intermediate-acidic complexs of the Yanshanian and their surrounding wall rocks of the Neoproterozoic to Cambrian. The mineralization is jointly controlled by magma, strata lithology, structure and wall rock alterationr. Ore-forming magmas were drived from the deep mantle and were contaminated by the crust to some degree during their ascending process. The calc-alkali complexs are typically porphyrite or porphyry and show characteristics of adakite-like rocks in chemical composition. The ore-bearing strata are mainly carbonate rocks, and their sound physical and chemical characters provided favorable wall rock conditions for mineralization. The location of the ore-forming intrusions were controlled by the intersecting places between the NW and NE or the NW and NEE trending fault structures. The ore-controlling and ore-bearing structures mainly include contact zone, xenoliths structure, interlayer fractured zone and unconformity structure, etc. The mineralization intensity, the orebody thickness and the spatial distribution of different ore types were mainly controlled by skarnization of the wall rocks.Sulfur, carbon, lead, hydrogen and oxygen isotopic studies indicated that S and C in the ore were mainly derived from the mantle magma and Pb was characterized by anomalous lead containing superfluous radioactive lead. The radioactive lead may come from crystalline basement of the late Archean. The ore-forming fluids were mainly magmatic hydrothermal fluids, though some meteoric water might be added during later mineralization stage. Detailed study on fluid inclusions indicated that the homogenization temperature and salinity of the ore-forming fluids declined from the early to late mineralization stage, and the mineralization occurred under the epithermal conditions of 1.7~0.6 km. During the oxide and the quartz-sulfide stages when the main ore minerals were precipitated, the ore-forming fluids had gone through an immiscible process (boiling) that may have caused the precipitation and concentration of Au, Cu, and.The integrated study suggested that the Yinan gold deposit presented some metallogenic laws on the aspects of ore-concerning magmas, strata, ore-controlling structures, wall rock alteration and zonation, mineralization types and their spatial combination, ore-forming and denudation depth, etc. Some prediction indicators of magmatic rocks, strata lithology, structures, geophysics, place names and mining relics were confirmed and applied to the metallogenic prediction on the entourage of the mine. Two new targets are delimited in the Liangquanzhuang and Xichaoyang areas around the mine. Ores were found by drilling project attestation in both areas, which exhibited a nice future for the further ore exploration of the Yinan gold deposit.