The cassiterite-anatase-ilmenite-monazite-sulphide-chlorite assemblage of North Tincroft Lode
Geoscience in South-West England
North Tincroft Lode (New Cook's Kitchen Mine) forms a segment of an ENE-WSW-striking lode structure that can be traced for similar to2 km along strike and similar to800 m vertically through the Camborne-Redruth mining district, Lode samples from previously undescribed shallow workings between deep and shallow adit levels (similar to28-45 m below surface) have been analysed by optical microscopy, SEM and XRD, and reveal a complex polymetallic mineralogy, Cassiterite, arsenopyrite, chalcopyrite and sphalerite galena inclusions) occur in a dense, non-brecciated, chlorite fluorite quartz matrix and are accompanied by significant monazite, anatase and ilmenite. All phases are fine-grained (< 200 gm diameter) and the paragenetic relationships suggest rapid, telescoped, infilling of the lode by cassiterite, monazite and ilmenite, in a matrix of sulphides and chlorite. Vugs within the matrix contain euhedral single crystals, twins and intergrowths of anatase and monazite, with less common cassiterite, chalcocite, chalcopyrite, bornite, cuprite, ilmenite, goethite. langite, brochantite, marcasite, arsenopyrite, pyrrhotite, sphalerite and apatite. The North Tincroft Lode, with its cassiterite-sulphide-chlorite assemblage, is faulted by Pryce's Lode at the 175 fathom level (similar to320 metres below surface). The mixing between magmatic-hydrothermal and meteoric fluids previously inferred to generate such assemblages must therefore have occurred early in the mineralisation history and was possibly coeval with development of cassiterite-tourmaline assemblages at depth.
Vol. 10, pp. 50 - 57
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