Rocks composition

Several sub-classification.s of epithermal preciou.s-metal deposits have been proposed mineralogy, host-rock composition and elemental association (Lindgren, 1928), gold-silver ratios of metal weights (Ferguson, 1929 Nolan, 1933), mineral paragenesis (Nishiwaki et al., 1971), and production ratios of metals (Heald-Wetlaufer et al., 1983). 

Figure 1.199. Plot of K2O versus Si02 for volcanic rocks thought to be genetically related to Au mineralization. High sulfidation (HS) deposits appear to be associated with a narrow range of igneous rock composition, dominated by dacite and andesite. Low sulfidation (LS) deposits are largely associated with andesite and rhyolite, but major deposits such as Ladolam, Porgera and Cripple Creek are associated with shoshonitic and alkalic rocks (Hedenquist et al., 1996).

The bulk rock composition vector is a linear combination of the mineral compositions (equivalently, the mixture composition vector is a linear combination of the end-member composition vector). The non-negative coefficients of this linear... 

Find the projection y of the rock composition x given in weight percent in Table 2.2 into the diopside-olivine-silica triangular diagram of Walker et al. (1979). This diagram uses coordinates given by ... 

This projection step first consists in recasting the molecular rock composition as linear combinations of the mineral molar coordinates pl-di-ol-si. The results represent a modified rock vector m+ related to m through the matrix Q, such that... 

The matrix PQM can be computed once and used for any further calculation. In order to compute the coordinates ynorm of the rock composition in the triangular diagram, the solution y should finally be normalized to 1. The result is... 

The concept of metric tensor becomes central whenever distances and projections are considered, particularly when least-square criterion are used, a point that will be discussed in Chapter 5. Let us ask the frequently raised question of how to find an expression in terms of old coordinates (e.g., oxide proportions) for a projection made in the non-Euclidian space. This could be the case for finding oxide abundances of a basalt composition projected in the Yoder and Tilley tetrahedron, or the oxide abundance of a metamorphic rock composition projected into an ACF diagram assuming that quartz is present. 

A rock is made of 0.45 moles Si02,0.10 moles CaO, and 0.45 moles MgO, which we will describe with the composition vector v (0.45,0.10,0.45). If we consider this rock as being made of virtual forsterite (Si02, 0, 2MgO), enstatite (2Si02, 0, 2MgO), and diopside (2Si02, CaO, MgO), what is the projection vector v of the rock composition onto the enstatite-diopside plane ... 

In the virtual mineral space, the rock composition is projected onto the plane made by the vectors enstatite [0,1,0]T and diopside [0,0,1]T. Although these vectors are not orthogonal in the original oxide composition space, which can be verified by constructing the dot product of columns 2 and 3 in the matrix BT, the particular choice of the projection makes the vectors orthogonal in the transformed space. According to the projector theory developed above, we project the rock composition onto the column-space of the matrix A such that... 

We find the projected rock composition v by applying the change of variable backwards... 

Figure 12. Linear regression of chondrite data in A Mg vs. 5 Mg space compared with the whole-rock composition of an Allende CAI.

Pyroxenes (as feldspars) occupy a position that is chemically central in the realm of rock compositions (Robinson, 1982). They are therefore found ubiquitously and virtually in any kind of paragenesis developing in the P-T-Xconditions typical of earth s mantle and crust. Table 5.31 hsts the main occurrences. 

Fig. 2. Correlation between a field of rocks compositions of the bimodal complex and the fields of intraplate magmatic rocks in the Central Asia and typical magma sources by primary isotope compositions of Sr and Nd. Fields of rocks explore bimodal complex -1, Early Mesozoic -2 and Late Mesozoic -3 of Central Asia. Correlation trend of basalt composition of the bimodal series of the Early Mesozoic Mongol - Transbaikalian region (Yarmolyuk et al. 2002) -4. At drawing of the diagram we used the data from the work (Magma types, 2006). PREMA and BSE values (Zindler Hart 1986), Siberian plume (Sharma etal. 1992).

In order to determine the source composition of sediments using trace elements, it is necessary to ascertain that the element is immobile under conditions of diagenesis and weathering (Spalletti 2008). Several ratios and plots may be used to define the source rocks. The felsic source rock compositions are found in the Co/Th vs. La/Sc diagram (Fig. 3 Table 1). Other trace element characteristics of sedimentary rocks also place some constrains on the nature of the source rock. Floyd Leveridge (1987) used a La/Sc vs. Hf plot to discriminate between different source compositions. In this plot, most data fall in the felsic source to mixed felsic/basic source field (Fig. 4 Table 1). 

Whole-rock compositions were determined by XRF and solution ICP-MS using the methods outlined by Yu et al. (2001) and Robinson (2003). 

Fig. 2. Whole-rock compositions plotted on an (Na+K)/AI versus (Fe+Mg)/AI MER diagram.

The direction of long-term changes in rock composition due to the action of groundwater can be determined by thermochemical calculations of the equilibria between various possible constituents (8). Appropriate thermochemical data are required. Exper-... 

Prototype LIBS sorting system is firstly developed by International Technologies Lasers (ITL) Company. In present modification, the system accomplishes evaluation of conveyed rocks composition. Beta site test was successfully accomplished at 2004 on Four Corners Mine, Florida. 

Table 13.1 Representative rock compositions from in-situ measurements by Mars rovers ...

The crust of Mars is basaltic, with only small amounts of other rock compositions. Most volcanism was ancient but some eruptions, especially in Tharsis and Elysium, may extend to the present day. 

Lodders, K. (1998) A survey of shergottite, nakhlite and chassigny meteorites whole-rock compositions. Meteoritics and Planetary Science, 33, A183-A190. 

Estimated compositions ofthe giant planets are given in Table 14.3, normalized to the solar composition. The relative proportions of rock and volatiles are estimated from mean densities, the rock compositions are assumed to be chondritic, and the ratios of hydrogen to helium are derived from spectroscopic or spacecraft measurements of atmosphere compositions. 

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