The feeder zone to the Lokken ophiolite-hosted massive sulfide deposit and related mineralizations in the central Norwegian Caledonides

• DOI: 10.2113/gsecongeo.84.8.2173
• Publication Date: 2009-04-03T13:35:40Z
• Authors: Tor Grenne
• Keywords: Norwegian

The Lokken orebody is situated within a 1- to 2-km-thick Lower Ordovician metavolcanic sequence of ophiolitic affinity. deposit probably the largest ophiolite-hosted massive sulfide body in world and originally contained 25 30 million metric tons ore. It has primary elongated morphology; shape was largely controlled by its sheetlike, fissure-related, hydrothermal feeder zone which underlies central part stratiform along entire length. very well defined down at least 300 m below contemporaneous paleosea floor.The main zone, with width approximately 100 m, comprises vein stockwork disseminations. increases density toward most 40 50 particularly ore level. Host volcanites have suffered pervasive Fe-rich chlorite + quartz alteration. Close level, sericite gradually becomes more prominent expense chlorite.Outside content decreases rapidly, moderate alteration host albite or - epidote assemblages, containing Fe Mg-rich chlorites. general mineralization paragenesis interpretation evolution (1) early precipitation, 130 wide, fine-grained dirty pyrite sphalerite thin veins as void fillings disseminations, resulting from mixing ascending solutions seawater--later wall rocks produced albite; (2) partial sealing upflow due precipitation sulfides, followed overgrowth coarse-grained on formed sulfides wide; (3) replacement earlier chalcopyrite dissolution chlorite-quartz near-primary solutions; (4) selective formation residual zone; (5) chalcopyrite, SiO 2 , subordinate fracture during declining stages activity.The consistent Mg enrichment altered suggests either that were bearing they had gained influx normal ambient seawater deeper zone. Furthermore, data show that, some stage, undersaturated respect silica Zn, Cu, Fe.In parts system, amount precipitated than four times immediately overlying Isolated feeder-type uppermost gabbro through lower pillow lava considered represent nearly total loss metal load their ascent sea-floor crust. suggested zones, cooling seawater, may exerted significant control composition size associated deposit.