Ore petrology and applied mineralogy of the Trout Lake massive sulfide deposit, Flin Flon, Manitoba

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Healy, Raymond E.
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The ore mineralogy of the Trout Lake massive sulfide deposit, Flin Flon, Manitoba has been investigated. Nine ore types are defined, of which seven form a differentiation series from the Zn-rich hangingwall ores to the Cu-rich footwall ores. The remaining two ore types are of tectonic origin. Two groups of elements: (1) the Zn-Group (Zn, Cd, Sb, Pb, Ag, Hg, In, Sn and As), and (2) the Cu-Group (Cu, Se, Te, Co, and Fe) form the principal geochemical associations of the ores. Twenty six ore minerals including sulfides, oxides, sulfosalts, sulfantimonides, alloys, intermetallic compounds, tellurides and selenides have been identified. The principal Zn- and Cu-minerals are sphalerite and chalcopyrite, respectively. Twelve Ag-bearing minerals were identified or inferred, of which sulfosalts and tellurides account for<24% of the Ag, Au-Ag-Hg alloy for <19% of the Ag, and galena for 3% of the Ag in the ore. Chalcopyrite, pyrite and sphalerite are inferred to contain 45, 11 and 55ppm Ag, respectively, corresponding to 23, 14 and 19% of the Ag in the ore. The average composition of Au-Ag-Hg alloy (in wt%) is 49.2% Ag, 38.7% Au, 11.0% Hg and 0.70% Fe. 'Invisible' Au in pyrite (0.72ppm Au) and arsenopyrite (30.2ppm Au) account for 6 and 1%, respectively of the Au in the ore; 93% occurs as Au-Ag-Hg alloy. From image analysis determined grain size data, minimum grinds for liberating sphalerite, chalcopyrite, pyrite, galena and freibergite are calculated as +208um, -175um, -95um, -48um and -60um, respectively. Similarly, the optimum grinds for liberating the above minerals are -52um, -52um, -26um, -9um and -5um, respectively. Predicted minimum liberations are 73% for sphalerite, and 69% for chalcopyrite. Two textural types of Au-Ag-Hg alloy are recognized: (1) inclusions, grain coatings on, interstitial-fillings and fracture-fillings in, pyrite; and (2) large (<5mm) anastomosing masses. The losses of Au to the tailings are due largely to extremely fine-grained Type 1 Au-Ag-Hg alloy entrapped in pyrite (64%), and Au in solid solution in pyrite and arsenopyrite (36%). The principal Ag losses to the tailings are largely due to Ag in solid solution in pyrite, and poor recovery of pyrargyrite. The environmentally hazardous elements As and Hg are largely rejected to the tailings, and backfilled underground. Chalcopyrite Stringer and Disseminated Pyrite + Chalcopyrite ore types represent tectonically flattened feeder pipe mineralization. Vein Quartz + Chalcopyrite ore type is evidence of limited sulfide mobilization during metamorphism. Diablastic texture, characterized by myrmekitic intergrowths of chalcopyrite, sphalerite and pyrrohotite was produced by a quartz-diorite intrusion of the large Lens 2 of north zone. This texture is not amenable to grinding, and may yield middling particles of chalcopyrite and sphalerite, which will be recovered in the Cu-concentrate.