Ultramafic rocks

The literature data presented in this chapter represent a wide variety of metamorphic rock types including metabasites, metapelites, marbles, calc-silicate rocks, ultramafic rocks, and metagranites. Hydrothermal or low-temperature apatite occurrences were not considered for this chapter. 

Feux, A. N. and Baker, D. R. (1973). Stable carbon isotopes in selected granitic, mafic, and ultramafic igneous rocks. Geochim. Cosmochim. Acta 37, 2509-2521. 

Valuable mineral deposits which form by residual concentration pertain to iron, manganese, aluminum, nickel, clays, tin and gold. Aluminum comes almost exclusively from residual concentrations of bauxite, which result from the laterihsation of alumina rich igneous rocks like syenites under tropical and subtropical climatic conditions. Laterites also contribute nearly 80% of the world s reserves of nickel at grades better than 1% Ni. They form by residual concentrations as a result of weathering of mafic and ultramafic igneous rocks, which are relatively enriched in nickel. 

Northern Californian soils have higher concentrations of Cr, Co, Cu and Ni than southern California since there are volcanic ultramafic rocks in northern California. Ultramafic rocks are mostly serpentine, a magnesium silicate with associated high amounts of Ni and Cr. Soils formed on serpentine parent materials contain high to extremely high Ni and Cr concentrations in soils. Soil parent material is a factor mostly controlling trace element concentrations in soils. 

In addition to anthropogenic pollution, some serpentine soils derived from Fe and Mg-rich ultramafic rocks are enriched in Ni, Cr and Co. In North America, ultramafic rocks form two discontinuous bands along the east and west side of the continent. The largest area of ultramafic terrain is in the Klamath Mountains province of northern California and southern Oregon (Lee et al., 2001). Serpentinite is a metamorphic rock formed from low... 

Worldwide distribution of magnesium-rich ultramafic rocks. 

Goff, F. and Lackner, K.S., Carbon dioxide sequestering using ultramafic rocks, Environ. Geosci., 5(3), 89,1998. 

Our results demonstrate significant spatial differentiation in the geochemistry of Sacramento Valley soil between the eastern and western sides of the valley that is related to the geomorphic separation of the valley by a levee along the Sacramento River. The western valley contains an elevated component of material derived from ultramafic rocks compared to the eastern side. 

This east-west difference reflects dominance in sediment source in the eastern valley by material derived from glacial debris and placer mining, and the presence of ultramafic rocks in the headwaters of western streams and ultramafic constituents in sediments on the west side of the valley. 

The Ulsan carbonates (Fig. 1) have long been interpreted as limestone of Paleozoic age or "age unknown" and as the host of a skarn-type iron (magnetite) deposit due to the intrusion of Cretaceous granitic rocks (Park Park 1980 Choi et al. 1999). However, a Paleozoic marine limestone hypothesis fails to explain the spatial association or the relationship between carbonate and ultramafic rocks in a concentric, ellipsoidal shape surrounded by Cretaceous sedimentary, volcanic, and granitic rocks. The sedimentary hypothesis also fails to explain the isolated exposure of a funnel-shaped Paleozoic marine limestone where no marine limestone has been previously observed within the Mesozoic Kyongsang Basin. 

Geological Setting The geology of the study area consists of Cretaceous sedimentary, volcanic, granitic, ultramafic (serpentinite), and carbonate rocks containing a magnetite-rich pipe and basic dykes (Fig. 1). The sedimentary rocks are intruded by felsic volcanic, granitic and ultramafic rocks,... 

The geology of Cyprus is dominated by four distinct terranes - the Troodos Ophiolite Complex composed of mafic and ultramafic rocks, the Circum-Troodos Sedimentary Sequence containing calcarenites, siltstones and carbonates, the Mamonia Complex composed of igneous, sedimentary and metamorphic rocks and the Kyrenia Terrain containing a series of allochthonous massive and recrystallised limestones dolomites and marbles. These terranes generate highly varied landscapes (Fig 1). 

The Stillwater Complex consists of a sequence of differential layers of mafic and ultramafic rocks, which extend for a strike length of up to 40 km and has a maximum exposed thickness of about 7.4 m [3], There are several mineralization zones at the Stillwater Complex, including a PGM-rich zone and a low-grade zone. The Stillwater ore that is processed nowadays contains olivine, plagioclase, as well as plagioclase-brauzite, all of which are naturally hydrophobic gangue minerals. 

Xenoliths from Siberian continental lithosphere, with Archean model ages, had b Li as low as +0.5 (Eouman et al. 2000). If these values accurately represent the Archean mantle, they suggest the potential for Li isotopic evolution in the Earth, from lighter compositions in the ancient mantle to what is seen in present-day MORE. In spite of the analytical challenges presented by ultramafic rocks, more data from these materials are crucial to an understanding of Li in the mantle, and in resolving questions about the appropriateness of the accepted MORE mantle range. 

Chromium is a compatible element in the Earth s mantle, and tends be present in much greater concentrations in mafic igneous rocks than in felsic ones (Faure 1991). Ultramafic rocks often contain over 1,000 ppm Cr and can generate environmental problems when they weather (Robertson 1975 Robles and Armienta 2000). Granites may contain less than 20 ppm Cr, whereas shales contain roughly 90 ppm. 

Enstatite-bronzite (MgTel Si O, Gabbros Mg-iich ultramafic rocks serpentinites meteorites... 

Fe2Si206 < 0.5 ultramafic rocks andesites rocks with high-P metamorphism... 

Diopside-hedembergite (Ca,Mg,Fe)2Si206 Cr-rich ultramafic rocks contact metamorphism (cipollines, comubianites)... 

Augite (Ca,Mg,Fe,Al)2(Si,Al)206 Basalts, andesites, tephrites, limburgites gabbros, dolerites, ultramafic rocks. Sometimes in granites... 

Wenner D. B. and Taylor H. P. Jr. (1971). Temperatures of serpentinization of ultramafic rocks based on fractionation between coexisting serpentine and magnetite. Contrib. 

The Big Lake Cu-Zn-Ag-Au voicanogenic massive sulphide (VMS) occurrence is hosted in mafic-ultramafic strata of the Schreiber-Hemio greenstone belt near Marathon, Ontario (Fig. 1). This VMS is unusual in that it is one of a few documented VMS occurrences in sequences lacking felsic volcanic or volcaniclastic rock. 

The VMS sulphides define a broadly conformable sheet 5-50 m below the base of the BLUC. This synformal surface of mineralisation generally coincides with the transition from ultramafic cumulates and strongly foliated metavolcanic rocks to an underlying sequence of metavolcanic rocks and interflow metawacke and metasiltstone rocks (Fig. 2). Sphalerite-pyrrhotite mineralisation in hydrothermal veins was also observed within the BLUC several km west of this study area. 

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