Intrusion-related Gold Deposits of North China Craton, People's Republic of China

摘要

Intrusion-related gold deposits are widely distributed within the North China craton or along its marginal fold belts. Presently, about 200 individual intrusion-related gold deposits (prospects) have been discovered, among which Yuerya, Anjia-yingzi, Linglong, Jiaojia, Chenjiazhangzi, Qiyugou, Jinjiazhuang, Dongping, Hougou, Huangtuliang, Guilaizhuang, Wulashan and Donghuofang are the most important ones. In general, the intrusion-related gold deposits can be classified into three major groups according to their host rocks: (1) hosted by or related to felsic intrusions, including (la) calc-alkaline granitoid intrusions and (Ib) cryptoexplosion breccia pipes; (2) related to ultramafic intrusions, and (3) hosted by or related to alkaline intrusions. The first group contains the Yuerya, Anjiayingzi, Linglong, Jiaojia, Chenjiazhangzi and Qiyugou gold deposits. Gold mineralization at these deposits occurs within Mesozoic Yanshanian calc-alkaline granitoid intrusions or cryptoexplosion breccia pipes as gold-bearing quartz veins and replacement bodies. Pyrite, galena, sphalerite, chalcopyrite, native gold and electrum are major metallic minerals. The Jinjiazhuang deposit belongs to the second group, and occurs within Hercynian diopsidite and peridotite as quartz veins and replacement bodies. Pyrite, marcasite, arsenopyrite, native gold and electrum are identified. The third group includes the Dongping, Hougou, Huangtuliang, Guilaizhuang, Wulashan and Donghuofang deposits. Gold mineralization at these deposits occurs predominantly within the Hercynian alkaline intrusive complexes as K-feldspar-quartz veins and replacement bodies. Major metal minerals are pyrite, galena, chalcopyrite, tellurides, native gold and electrum. All these pyrite separates from Hercynian and Yanshanian intrusions or cryptoexplosion pipes associated with the gold deposits show a broad range in delta~(34)S value, which is. overall higher than those Precambrian rocks and their hosted gold deposits. For the alkaline intrusion-related gold deposits, the delta~(34)S values of the sulfides (pyrite, galena and chalcopyrite) from the deposits increase systematically from orebodies to the alkaline intrusions. All of these intrusion-related gold deposits show relatively radiogenic lead isotopic compositions compared to mantle or lower crust curves. Most lead isotope data of sulfides from the gold ores plot in between the fields of the intrusions and Precambrian metamorphic rocks. Data are interpreted as indicative of a mixing of sulfur and lead from magma with those from Precambrian metamorphic rocks. Isotopic age data, geological and geochemical evidences suggest that the ore-forming materials for the intrusion-related gold deposits were generated during the emplacement of the Hercynian or Yanshanian intrusion. The calc-alkaline or alkaline magma may provide heat, volatiles and metals for the intrusion-related gold deposits. Evolved meteoric water, which circulated the wall rocks, was also progressively involved in the magmatic hydrothermal system, and may have dominated the ore fluids during late stage of ore-forming processes. Therefore, the ore fluid may have resulted from the mixing of calc-alkaline or alkaline magmatic fluids and evolved meteoric water. All these intrusion-related gold deposits are believed to be products of Hercynian or Yanshanian calc-alkaline and alkaline igneous processes along deep-seated fault zones within the North China craton or along its marginal belts.