摘要:
查岗诺尔铁矿是西天山阿吾拉勒铁成矿带的一大型磁铁矿床,赋存于石炭系大哈拉军山组火山-沉积岩系,根据矿石组构和矿物组合特征,可以划分为岩浆期和热液期(包括矽卡岩亚期)两个成矿期。该矿的矿床地球化学研究比较薄弱,本文针对不同成矿阶段的磁铁矿、黄铁矿、黄铜矿和方解石,利用同位素质谱测试方法,开展C、O、S等稳定同位素特征研究。结果表明:从岩浆期到矽卡岩期,磁铁矿的δ18OSMOW主要表现出岩浆热液的特征,但呈降低的趋势(2.4‰~1.9‰),指示围岩蚀变等热液活动对成矿流体的改变;岩浆成矿期和矽卡岩期δ34SV-CDT主要显示岩浆来源(0.8‰~7.3‰),但岩浆期可能有少量地层硫或海水硫的混入(δ34SV-CDT>10‰);成矿晚期阶段的方解石δ13CPDB-δ18OSMOW呈正相关,指示可能存在不同类型NaCl浓度混合或流体-围岩之间的水岩反应,大理岩为成矿作用提供了部分的成矿物质。研究认为成矿早期以岩浆流体的结晶分异作用为主,而晚期阶段矽卡岩化及其退蚀变作用是铁富集成矿的主导因素。
Abstract:
Situated in the Awulale metallogenic belt of Western Tianshan, the large-sized Chagangnuoer magnetite deposit is contained within volcanic-sedimentary rocks of the Carboniferous Dahalajunshan Formation. According to ore fabrics and mineral assemblages, the mineralization events of this deposit were divided into the magmatic stage and the hydrothermal stage (including the prograde sub-stage). Due to the lack of studies in ore deposit geochemistry for this deposit, this paper aimed to conduct systematic stable isotope analyses of C, O and S by isotope mass spectrometry method for minerals of magnetite, pyrite, chalcopyrite and calcite chosen from various mineralization stages. Those data indicated that δ18OSMOW values of magnetite mainly showed a magmatic hydrothermal feature, and a decreasing trend (1.9‰-2.4‰) from the magmatic stage to the prograde stage, which reflected that wall rock alteration may change the compositions of ore-forming fluid. Both the sulfur isotopic components (0.8‰-7.3‰) at the magmatic stage and prograde stage were predominantly the magmatic feature. However, a small amount of S from strata or sea water was mixed into the ore-forming fluid in the magmatic stage as the δ34SV-CDT was larger than 10‰. During the late ore-forming stage, the δ13CPDB-δ18OSMOW ratios of calcite showed a positive linear correlation, probably attributing to the mixture of different concentrations of NaCl fluid or the water-rock reaction between ore-forming fluid and wall rocks. The partial mineralization materials were derived from marble wall rock. Therefore, crystallization differentiation of magmatic fluid was the dominant mineralization on the early ore-forming stage, whereas prograded and retrograded alterations were the crucial factors in iron enrichment and mineralization on the later stage.
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