Fluid inclusion chemistry as a guide to tin mineralization in the Dartmoor granite, south-west England

Abstract

Sixty-two quartz samples were separated from stream sediments draining the Dartmoor granite (southwest England) and chemically analyzed using the ICP-linked decrepitation technique. The samples were derived from three environments: an area of granite peripheral to the mineralized area, and a region of granite-devoid of mineralization. On a local scale, the fluid inclusion decrepitates in samples from the mineralized region show relatively higher concentrations of Rb, B, Sn, Cu, and S, and lower concentrations of Na, K, Ca, Fe, Li, Ba, Sr, and Zn. Principal component analysis of the whole multi-element data set confirms that the elements Rb, B, Sn, Cu, and S behave independently from the major constituents of the fluid inclusion decrepitates (Na, K, Ca, Fe, etc.), and possibly represent a “mineralization” factor. Discriminant function analysis, using the concentrations of Na, Ca, S, Ba, Sr, and Rb, is able to produce an efficient separation of the samples into the three groups. The regional variation in chemistry of the fluid inclusion decrepitates can be explained by invoking two main sources of quartz for the stream sediments: quartz veins associated with the mineralization, and quartz from the unaltered granite. The fluids in quartz from the unaltered granite also seem to show a regional variation, as elevated concentrations of Na, K, Ca, Fe, and Zn are found in decrepitates from samples adjacent to the region of mineralization. The results of this study indicate that the multi-element chemical analysis of fluid inclusion decrepitates may be a viable method of geochemical exploration for granite-hosted tin deposits.