The geology and geochemistry of a Robinson Creek gold ocurrence, north of Amisk Lake, Saskatchewan
Hattie, Ian Edwin
The Robinson Creek Gold Occurrences, situated approximately, 12 kilometers southwest of Flin Flon, Manitoba, are of the typical quartz vein type. Mineralized quartz veins are contained within shear zones, hosted within rocks which may represent structurally deformed, metamorphosed and chemically altered, mafic volcanic flows and or related pyroclastic rocks of the Amisk Group volcanics. Metamorphosed intermediate to felsic volcanic rocks (dacite to rhyolite), also belonging to the Amisk Group, are found stratigraphically above the mafic volcanics, and may represent former volcanic flows and related pyroclastic rocks. These rocks are intruded by two varieties of porphyritic dacite to rhyodacite of contrasting age. The Amisk volcanic rocks are overlain by highly deformed conglomerates and rare sub-arkosic sandstone of the Missi Group sediments. Clasts in the conglomerate were probably derived from the underlying Amisk volcanics (Stauffer and Mukherjee, 1971). The Amisk volcanics probably represent a transition from tholeiitic to calc- alkaline chemical affinities (Fox, 1976, Walker and Watters, 1982) and perhaps from an ocean floor to an island arc setting (Stauffer, 1974). However, all of the rocks in the area have been affected by several phases of deformation and are metamorphosed to greenschist to lower amphibolite grade. Chemical alteration of the rocks has been enhanced be penetrative deformation, most noticeable in the Robinson Shear system which hosts the gold. The typical secondary assemblage is ferroan dolomite (ankerite), quartz, chlorite, muscovite (sericite), pyrite and locally tourmaline. Carbonate alteration (ankerite), predates the introduction of the gold-bearing quartz veins in the sheared mafic volcanics. Metasomatic alteration of the mafic rocks associated with gold mineralization is typified by an enrichment in Rb, Sr, and K and depletion in Na, Ca, and variably Mg. Metasomatism is generally associated with a volume increase in sheared rocks and a volume reduction in rocks with minor penetrative deformation. The gold-bearing quartz veins are interpreted to be in a dilatent zone hosted within two shear zones located near the hinge of a tightly closed anticline with a steeply dipping axial surface.