Abstract

The Cleveland tin-copper deposit comprises several lenses of pyrrhotite-cassiterite-stannite-chalcopyrite mineralization represented by a series of interlayered chert-shale beds and mineralized units occurring within an Early Cambrian succession of spilitic basalt, mafic pyro-clastic, argillite, chert, and limestone overlain by a sequence of micaceous turbiditic graywacke and argillite. South and east of the deposit is the Late Devonian Meredith Granite.Ore paragenesis is divided into four stages with a superimposed mineralogical zonation: (I) quartz + fluorite + wolframite + molybdenite + (cassiterite) as stockwork veins in the footwall rocks; (II) quartz + tourmaline + fluorite + chlorite + pyrrhotite + chalcopyrite + cassiterite + stannite as stratabound lenses parallel to the host rocks, with sphalerite and arsenopyrite common at the extremities of the sulfide lenses and quartz veins with sphalerite, arsenopyrite, chalcopyrite, and galena surrounding the deposit; (III) quartz + arsenopyrite + (stannite) as veins; and (IV) fluorite + carbonate + quartz filling veins and vugs. An extensive alteration halo in the hanging wall of the sulfide lenses is defined by increased replacement of pyroxene by actinolite nearer to the ore, accompanied by an increase in K, Rb, Sn, and Zn and a decrease in Na, but is not reflected by the whole-rock delta 18 O values.Fluid inclusion and stable isotope data reveal a systematic trend in depositional temperatures and a marked consistency in composition of the hydrothermal fluid. Fluids of stages I and II were low to moderately saline (8-14% NaCl), but while stage I fluids were of low CO 2 content, the CO 2 content of stage II fluids was locally high. The CO 2 in stage II fluids was probably derived from dissolution of limestone. The salinity of the fluid decreased slightly to 7 to 11 percent NaCl and was very low in CO 2 during stage IV. Fluid temperatures are estimated at about 480 degrees C for stage I and 500 degrees C for stage II, and 250 degrees to 300 degrees C during stage IV. The calculated delta 18 O composition of the water in the hydrothermal fluid was about 8.7 per mil for stage I, 10.2 per mil for stage II, and 9.5 per mil for stage IV. The delta 34 S values of the sulfides were near to 0 per mil (-0.2 to +5.5 per mil) throughout the mineralization. The consistent salinity and the isotopic compositions indicate a magmatic source for the mineralizing fluid and a lack of mixing with meteoric water.The Cleveland deposit originated from the metasomatic replacement of limestone beds by tin-bearing, low to moderately saline fluids of initially low CO 2 content derived from a granitic source related to the Meredith Granite.

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