Abstract:
The Maliping large-scale Pb-Zn deposit (~6.0Mt @13.4% Pb+Zn) is hosted in siliceous dolomite of the Lower Cambrian Meishucun Formation, which is one of the representative deposits of the Pb-Zn metallogenic district in Northeast Yunnan Province, China. Quartz is the major gangue mineral of the Maliping deposit, and its formation has lasted throughout the whole age of the mineral formation. Detailed mineral researches demonstrate that quartz of three stages was found in Maliping. Stage Ⅰ quartz is fine-grained and subhedral, associated with fine-grained pyrite and sphalerite; stage Ⅱ quartz is medium-coarse-grained and subhedral, associated with coarse-grained sphalerite and galena; and stage Ⅲ quartz is relatively pure. In general, the variation of quartz cathodoluminescene intensities from early to late stages of the Maliping deposit is closely related to the variation trends of Al, Ge, Li, Na and K contents, which implies the controlling effects of the trace elements over quartz cathodoluminescene intensities. The correlation among the elements suggests that trace elements in quartz enter the lattice mainly as single-atom substitution (Ge
4+→Si
4+) and compensatory substitution (Al
3+ +Li
+/Na
+/K
+→Si
4+). In addition, the large amount of Al and extremely small amount of Ti in the quartz from the Maliping deposit are characteristic of low-temperature hydrothermal deposits, which differs from those of the magmatic-related hydrothermal deposits. The variation of Al concentration in quartz has a general trend of increase from Stages Ⅰ to Ⅱ and decrease from Stages Ⅱ to Ⅲ, which reflects that the solubility of Al increases first and decreases afterwards, and which also implies that the mineralization is formed during the processes with fluid pH decreasing first and increasing later. Hence, the in-situ trace element composition of quartz is helpful to understand the genesis of hydrothermal deposits and the evolution of ore-forming fluids.