| Abstract:Situated in Xianghuangqi synelinore of Late Hercynian Tianshan-Inner Mongolian folded belt, the Hadamio gold deposit consists of two major orebodies which are now being exploited. One is composed of quartz, tourmaline, chalcopyrite, pyrite, magnetite, native gold and electrum and occurs extensively along the contact zone between the Hadamio granite porphyry and quartz diorite, associated with silicification, tourmalinization and beresitization; the other, which has the same mineral assemblage, is distributed inside the volcanic breccia dykes and associated with silicification, tourmalinization and epidotization. Of these wall-rock alterations, silicification and tourmalinization are intense and have close relationship with gold mineralization.The gold-bearing granite porphyry outcrop is about 80m long and 40m wide, trending west-east and dipping laterally in north and south directions. The major minerals include quartz，microperthite (Or87Ab13)，plagioclase(An =15—10) and biotite, the phenocrysts consist of K-feldspar, quartz and plagioclase, and accessory minerals are apatite, magnetite, sphene, zircon and hematite. The porphyry is characterized petrochemically by an average SiO2 of 71.92％and K2O+Na2O of 6.74％(with K2O/Na2O ratio being 1), thus belonging to nor real calc-alkaline rock series.A number of gold-bearing volcanic breccia dykes have been discovered around the tIadamio gold-bearing granite porphyry. Breccia dykes consist of granodiorite fragments, cataclastic quartz diorite and volcanic cements and have an average SiO2 of 72.31％and K2O+Na2O of 2.54％，with K2O/Na2O ratio being 0.5. The formation temperatures of minerals vary from 400℃ to 120℃ with those of the main ore-forming stage ranging from 190℃ to 282℃, averagely 210℃. According to the homogeneous temperature of fluid inclusions in quartz and formation sequence of minerals, the gold mineralization might be divided into four stages, i. e., quartz+tourmaline; quartz+chatcopyrite; polymetallic sulfides and carbonate+quartz. Oxygen, hydrogen, carbon and sulfur isotopic compositions suggest thatδ18O values of quartz from gold orebodies at the contact zone vary in a relatively narrow range(+9.8-13.5％), δ18OH2O values of equilibrium water are+4.8一 +6.9‰, δD values of fluid inclusion water in quartz are -46一-58‰, and δ34S values ot pyrite are+1.9- +2.6‰. The volcanic breccia dykes are characterized by mixed solutions with magmatic water as the major source. The stable isotope compositions are δ18O = +6.5- +9.0‰, δ18OH2O= +1.1- +3.7‰, andδD= -44 - -48‰, and the δ13C value(+7.1‰)of calcite is approximately equal to that of the gold orebody at the contact zone. The variation range of stable isotope values together with the behavior of minor elements in pyrite implies that sulfur, oxygen, carbon and some metallic elements were largely derived from igneous sources at depth. All the data mentioned above suggest that the granitoids originated from the anatexis of early Paleozoic eugoosynclinal volcanic-sedimentary rocks. Moreover, the gold-bearing porphyry and gold-dearing volcanic breccia dykes are products of the evolution of the same magmatic hydrothermal fluid at different stages. It is therefore considered that the studied gold deposit belongs geneticatly to the mesothermal gold deposit. |
