Publication details
A combined EMPA and LA-ICP-MS study of Li-bearing mica and Sn-Ti oxide minerals from the Qiguling topaz rhyolite (Qitianling District, China): The role of fluorine in origin of tin mineralization
| Authors | |
|---|---|
| Year of publication | 2015 |
| Type | Article in Periodical |
| Magazine / Source | Ore Geology Reviews |
| MU Faculty or unit | |
| Citation | |
| Web | Full Text |
| Doi | http://dx.doi.org/10.1016/j.oregeorev.2014.08.013 |
| Field | Geology and mineralogy |
| Keywords | Tin mineralization; Li-bearing mica; Cassiterite; Rutile; Fluorine; Immiscible fluid system; Qitianling |
| Description | The Sn-rich Qiguling topaz rhyolite dike intrudes the Qitianling biotite granite of the Nanling Range in southern China; the granite hosts the large Furong Sn deposit. The rhyolite dike is typically peraluminous, volatile-enriched, and highly evolved. Whole-rock F and Sn concentrations attain 1.9 wt.% and 2700 ppm, respectively. Cassiterite and rutile are the only Sn and Ti minerals; both cassiterite and Nb-rich rutile are commonly included in the phenocrysts. The Sn-Ti-F assemblage is pervasive, and contains spongy cassiterite in some cases; cassiterite also occurs in quartz veinlets which cut the groundmass. Electron microprobe and LA-ICP-MS compositions were used to study the magmatic and hydrothermal processes and the role of F in Sn mineralization. The presence of zinnwaldite and "Mus-Ann", which are respectively representative of early and late mica crystallization during magma differentiation, also suggests a significant decrease in f(HF)/f(H2O) of the system. Cassiterite included in the zinnwaldite phenocrysts is suggested to have crystallized from the primary magma at high temperature. Within the Sn-Ti-F aggregates, rutile crystallized as the earliest mineral, followed by fluorite and cassiterite. Spongy cassiterite containing inclusions of the groundmass minerals indicate a low viscosity of the late fluid. The cassiterite in the quartz veinlets crystallized from low-temperature hydrothermal fluids, which possibly mixed with meteoric water. In general, cassiterite precipitated during both magmatic and hydrothermal stages, and over a range of temperatures. The original fluorine and tin enrichments,f(HF)/f(H2O) change in the residual magma, formation of Ca,Sn,F-rich immiscible fluid, decrease of the f(HF) during groundmass crystallization, and mixing of magma-derived fluids with low-saline meteoric water during the late hydrothermal stage, are all factors independently or together responsible for the Sn mineralization in the Qiguling rhyolite. |