Genesis of the Zhengguang gold deposit in the Duobaoshan ore field, Heilongjiang Province, NE China: Constraints from geology, geochronology and S-Pb isotopic compositions

摘要

The Zhengguang gold deposit in the Duobaoshan ore field, hosted in volcanic rocks of the Middle Ordovician Duobaoshan Formation, is one of the largest gold deposits in the Northeastern Great Xing'an Range of the Central Asian Orogenic Belt (CAOB). The deposit comprises the No. I, II and III ore zones with a total resource exceeding 35 tonnes of Au, 100,000 tonnes of Zn and 100 tonnes of Ag. A genetic relationship between gold mineralization and concealed tonalite porphyry is inferred based on the characteristics of cryptoexplosive breccia and hydrothermal alteration indicative of porphyry-type and epithermal mineralization. Zircon LA-ICPMS U-Pb dating reveals that the tonalite porphyry was emplaced at 462.1 +/- 1.8 Ma (Middle Ordovician). The delta S-34(v-cur) values of sulfide minerals range from -3.0% to -1.7%0 with an average of -2.33% indicating that sulfur was mainly derived from a magmatic source. The Pb isotopic compositions (Pb-206/Pb-204 ranging from 17.572 to 17.629, (207)pb/(204)pb from 15.424 to 15.486, and Pb-208/Pb-204 from 37.206 to 37.418) suggest a major mantle component for Pb and, by inference, for other ore metals. Therefore, we suggest that the ore-forming elements in the Zhengguang gold deposit may be related to the mantle-sourced tonalite porphyry. On the basis of the geological characteristics and geochemical signatures documented in this study, we conclude that the Zhengguang gold deposit was formed in a porphyry to epithermal transitional environment associated with the concealed tonalite porphyry, as part of the Duobaoshan porphyry-epithermal ore system that is related to the subduction of the Paleo-Asian Ocean during the Ordovician. (c) 2017 Elsevier B.V. All rights reserved.