FLUID-ROCK INTERACTION AT CONTACT OF LINDSLEY-4B NI-CU-PGE OREBODY AND ENCLOSING GRANITIC-ROCKS, SUDBURY, CANADA

Part of the contact of the 4b Ni-Cu-platinum-group element (PGE) orebo dy, Lindsley mine, Sudbury, Canada, with the enclosing Murray granite is characterized by the presence of recrystallized and biotitic Sudbur y Breccia; in places the contact is faulted and sheared. In other area s of contact partly silicified granite contains disseminated chalcopyr ite and quartz-chalcopyrite veins with other minor minerals. Both ore and veins contain platinum-group minerals (PGM); predominant PGM are m ichenerite, kotulskite, merenskyite and sperrylite with gold, galena a nd Bitellurides. At some silicified-granite contacts Mn-rich garnets, some containing inclusions of PGM and quartz, are associated with biot ite + epidote + stilpnomelane + quartz. PGM as well as Au also occur w ithin Cl-rich biotite and ferropyrosmalite in massive sulphide and in siliceous ore. Quartz, chalcopyrite and feldspar in the contact rocks and in veins contain abundant, highly saline fluid inclusions. Standar d thermometry and analysis by scanning electron microscopy with energy -dispersive spectroscopy of the daughter minerals (NaCl, CaCl2, BaCl2, KCl and Fe-Mn hydroxychlorides) reveal that the fluids were trapped a t intermediate temperatures. The 4b orebody is surrounded by a sheath of brecciated granite (Sudbury Breccia) but is close to the Contact Su blayer; during and after emplacement of sulphide magma saline formatio nal fluid that was resident in the breccia interacted with hot massive sulphides in and near the Sublayer and remobilized Cu, Au and PGE. Th is fluid reacted with cooler rocks and ore in footwall fractures, enri ching the 4b protore and producing the adjacent Cu- and PGE-enriched q uartz veins. Exploration for Cu and PGE enrichment in footwall rocks o f the Sudbury South Range is warranted not only in zones of magmatic o re in the Contact Sublayer but also in fractures and permeable units w ithin Sudbury Breccia.