Chapter 1 - Global- to Deposit-Scale Controls on Orthomagmatic Ni-Cu(-PGE) and PGE Reef Ore Formation

Abstract

Large orthomagmatic Ni-Cu(-PGE) and platinum-group-element (PGE) deposits dominantly form during the assembly and peak of supercontinents, when mantle plumes bombard the Subcontinental Lithospheric Mantle (SCLM) roots. The thinner edges of thick resilient SCLM at (paleo)craton margins internal to continents focus mantle melting and transfer of melts into the crust via active translithospheric faults. An interconnected intrusive network provides the plumbing system to upper-crustal sites of deposit formation. Most PGE reef deposits form slightly inboard of margins at major subhorizontal crustal interfaces. Os isotope data are consistent with melt interaction with the SCLM, which may increase PGE contents of the melts. The degree of mantle melting, regional geodynamics, and interaction with lithospheric architecture determine the crustal setting, melt composition (High MgO versus Low MgO end-members), mechanisms of sulfide saturation, and deposit style. Tectonic stress switches can initiate dynamic injection of key ore-forming sulfide melts from deeper in the magmatic conduit system. Ore-forming concepts are translated into global- to deposit-scale exploration parameters.