Geochemistry of small differentiated intrusions and associated large igneous provinces: controls on the formation of magmatic sulfide ore deposits

English Abstract:

The formation of magmatic sulfide ore deposits is often considered to be the result of the saturation of mafic and ultramafic magmas in sulfur, and the formation of dense immiscible sulfide melts which segregate from the magma, concentrate metals, and form ore deposits. The triggers for saturation are widely considered to be contamination by the assimilation of S-rich crust, whereas the as important in the formation of world class ore deposits like Noril’sk. Several controls remain less well understood; viz: 1. Does the composition of the source and the depth of magma generation control mineral potential?; 2. Is the pathway of magma transportation an important control on ore formation?; 3. Are magmatic sulfides actually transported from the site of formation into the intrusions?; 4. What is the relationship of small differentiated intrusions to the large volumes of mafic magma that erupt in rift settings and as continental flood basalts?; 5. What relationships exist between ore formation and the stage of formation of large igneous provinces (LIPs)?

This presentation uses geochemical data for basaltic volcanic rocks and differentiated intrusions to look at process controls in the Siberian, Deccan, West Greenland, and Emeishan flood basalt provinces, the Keweenawan Mid-continent Rift (MCR), and the Nain Plutonic Suite (NPS). In the cases of the Deccan and NPS, composition of the source appears to control the availability of precious metals, nickel and copper. Mineralized differentiated intrusions in the Siberian Trap, MCR, and Emeishan occupy space created by trans-tension in strike-slip structural zones, and have geochemical and petrological features which support the emplacement of sulfide-laden magmas. The stage of formation of the mineralized intrusions often links to the early rifting and faulting of the crust in response to far-field tectonic events; this is illustrated by mineralized intrusions associated with the Siberian, West Greenland, and Emeishan LIPs. Although ore systems are genetically related to LIP events, the geochemical signatures of ore formation are found in discrete packages of comagmatic flood basalt erupted in depo-centers along the structural zones.