关键词: 铅锌矿床, 黄铁矿, 微量元素, LA-ICP-MS, 锡铁山

Abstract: The Xitieshan Pb-Zn deposit is located in the northern margin of Qaidam basin. Three type of ore bodies, that is, stratiform, veined and irregular were identified from the deposit in schist, marble and their transition zone. The Tangjianshan group, host rock of the deposit, is greenschist metamorphosed mafic to felsic volcano-sedimentary formation which deposited from late Ordovician shallow marine. There are many disputes about genetic types of the deposit, such as sediment-hosted Zn-Pb deposit (SEDEX), volcanic-associated massive sulphide deposit (VMS) and metamorphic overprinting exhalative sedimentary deposit. According to macro-and micro-observation on ore fabric, three main types of pyrite from stratiform ore bodies had been identified, that is, colloidal pyrite (Py-I), anhedral pyrite (Py-II) and subhedral-euhedral pyrite (Py-III), which could represent primary depositional pyrite, low level of recrystallized pyrite and high level of recrystallized pyrite, respectively. In this contribution, laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) was used to measure minor and trace element concentration for the above three types of pyrite, and obvious differences had been recognized. Metallogenic elements, such as Cu, Pb, Zn, Co, Ni and so on, are enriched in Py-I, Co/Ni> 1, and yield smooth time-space resolved signal of LA-ICP-MS analysis. Among them, Ni, Co and As might be situated in lattice of pyrite as solid solution, while Cu, Pb, Zn and other elements might exist in lattice（defect）of pyrite in form of nanometer mineral inclusions. Metallogenic elements in Py-II are variable and obviously lower than which in Py-I, and yield lots of pumps in time-space resolved signal of LA-ICP-MS analysis, indicating their existence of micrometer mineral inclusions in pyrite lattice. Metallogenic elements in Py-III are extremely low and generally below detection limit, except for some spot with minor amount of trace elements. Based on their occurrence and fabric characteristics, we assume that the Py-I was formed in the process of the submarine-exhalative sedimentation with volcanic activities, while Py-II and Py-III were produced from Py-I by later diagenetic and metamorphic
recrystallization in different degrees. Combined with recent studies of petrographic, zircon U-Pb geochronology, geochemistry and tectonic background of their host rocks, it is strongly suggested that the Xitieshan deposit should be a VMS, which had be undergone significant metamorphism of orebodies and reactivation of metallogenic elements during regional orogenic process after mineralization.

Key words: lead and zinc deposit, pyrite, trace elements, LA-ICP-MS, Xitieshan