| Lamasu copper deposit, located in the micro-continental block of Sailimu,northwest of Tianshan ore-forming belt, has receive much concerned and been studied deeply since discovered. However, considerable differences still exist between genetic type and ore-forming mechanism, apart from which, the ore-forming fluids are rarely studied. In this paper, after fabric and assemblage of the ores were studied based on the geology of the deposit, microthermometry and Laser Raman spectroscopy were used to conduct the study of fluid inclusions, which are the representative samples of ore-forming fluid, as well as the signal of determining the genetic type. Combined with the study of isotope, sulfide-EPM analysis and REE geochemistry, the genetic characteristics of the deposit were tried to be restricted.Mineralization-related porphyries are mainly plagioclase porphyry and granodiorite porphyry, and the latter may be the product of the emplacement of the consanguineous igneous magma in the late stage. The porphyries belong to typical calc-alkaline volcanic arc granite, forming in the continental arc environment and are the product of fractional crystallization, which experienced following process: partial melting after ocean crust subduction to the continental crust and replaced the original mantle wedge and mixed some lower crust.Quartz-sulfide mineralization stage is the most important stage for metal mineral formation, and divided into two sub-stages, early(I) and late(II) stages. The early stage of quartz sulfide (I) mainly develops massive pyrrhotite-pyrite- chalcopyrite ore and pyrite-chalcopyrite ores while the latter mainly disseminated, vein and patchy pyrite-chalcopyrite ores. Based on the observation and microthermometry, the system of the ore-forming fluids in I phase is H2O-NaCl-CaCl2 with a little CH4 while the latter changes into H2O-NaCl system, containing much CH4. The homogenization temperature in I-stage and II-stage is 271.2℃~ 330.7℃and 130.5℃~ 249.7℃, respectively while corresponding salinity is 6.01 ~ 13.94%(NaCl)and 3.2 ~ 13.94%(NaCl), respectively, with the density less than 1.00 g/cm3. Therefore, the ore-forming fluids in quartz-sulfide stage are low-dense, relatively reduced, medium to low temperature and salinity fluids. The study of C, H, O, S and Pb isotope shows that the ore-forming fluids in the I phase are mainly magmatic water while in the II phase were mixed with quantity of precipitation, C in in the II phase deprived from the solution of the limestone, S mainly originated from magma with part of strata mixed, and the ore-forming sources are derived from the mixture of the mantle and crust, resulting from the magmatism in the subduction belt. The EPM of the sulfide and REE geochemistry illustrate that the homogenization temperature is correct, and the reduce condition of ore-forming process is different.The factors of geologic background, ore-forming sources and ore-controlling structure lead to the conclusion that Lamasu copper deposit is a skarn-dominated porphyry - skarn deposit,closely related to the intermediate to acidic rocks.
|
PDF Full Text Request