Trace-Element Geochemistry and Petrogenesis of Barren and Ore-Associated Komatiites

The Aguablanca Ni–(Cu) sulfide deposit, SW Spain: geologic and geochemical controls and the relationship with a midcrustal layered mafic complex

“…Other variables such as the MgO, Ti0 2 , or Ce contents reflect the degree of fractional crystallization (Lightfoot et al 1990;. Thus, the La!Sm ratio vs the MgO or ThlNb can trace the role of fractional crystallization vs magma mixing or crustal contamination (e.g., Lesher et al 2001). As can be seen in Fig.…”

Erosion by flowing lava: geochemical evidence in the Cave Basalt, Mount St. Helens, Washington

“…Also, field evidence has been inferred in prehistoric tube-fed basalt flows in Washington, Oregon, Hawaii, and elsewhere (e.g., Greeley 1971;Greeley and Hyde 1972;Cruikshank and Wood 1972;Wood 1981;Coombs et al 1990;Greeley et al 1998) and in Precambrian channel-fed komatiite flows in Australia and Canada (e.g., Huppert et al 1984;Lesher et al 1984Lesher et al , 2001aLesher et al , 2001bHuppert and Sparks 1985;Groves et al 1986; Barnes et al 1988;McNaughton et al 1988;Evans et al 1989;Frost and Groves 1989;HoulØ et al 2002). However, much of the field evidence, especially in Precambrian komatiite flows, is equivocal.…”

Contrasting komatiite belts, associated Ni–Cu–(PGE) deposit styles and assimilation histories

“…Therefore, there is no intrinsic reason to imply that the crustal assimilation process is in itself crucial to the formation of large concentrations of magmatic sulfides. However, the nature of the contaminant and the role of magma recharge in the preservation of the assimilation signature may locally hinder the spatial and genetic relationship between ore localisation, evidence of crustal assimilation and the nickel sulfide ore formation process itself (Lesher et al 1999(Lesher et al , 2001). …”

“…Ore-genesis models have traditionally emphasised the role of crustal assimilation as a key factor in nickel sulfide ore-forming processes in komatiites (Lesher & Arndt 1995;Lesher et al 1999Lesher et al , 2001Barnes et al 2004). Upon emplacement, komatiites are thought to thermomechanically erode their substrate and assimilate significant crustal material (Lesher 1983).…”

“…The assimilation of iron oxide, silica, alumina and alkalies increases the polymerisation state of silicate melts, thus diminishing the number of available octahedral sites where sulfur is commonly coordinated (Irvine 1975;O'Neill & Mavrogenes 2002). Therefore, since komatiites are thought to erupt sulfide-undersaturated (Keays 1982(Keays , 1995Lesher & Groves 1986;Barnes & Fiorentini 2008), most researchers infer that crustal contamination plays a crucial role in lowering the sulfur capacity of komatiites and hence promoting ore genesis (Lesher et al 2001). …”