Magmatic concentration

The igneous processes which give rise to ore deposits are broadly classified into three types (i) magmatic concentrations and segregations, (ii) contact metasomatism, and (iii) hydrothermal processes. 

Table 1.6 Important types of magmatic concentration ore deposits.

An ore is a metal-bearing mineral that is valuable enough to be mined. Ore formation is primarily due to temperature and pressure effects (e.g., magmatic concentration, deposition upon cooling, evaporation, hydrothermal processes), weathering and transport phenomena (e.g., sedimentation, metamorphism, mechanical concentration, residual concentration), and chemical processes (e.g., abiotic and biotic oxidations, and reductions). These effects, phenomena and processes are illustrated in Figures 5.2-5.4. 

Indium (0.24 ppm) is similar in abundance to Sb and Cd, whereas T1 (0.7 ppm) is close to Tm and somewhat less abundant than Mo, W and Tb (1.2 ppm). Both elements are chalcophiles (p. 648), indium tending to associate with the similarly sized Zn in its sulfide minerals whilst the larger T1 tends to replace Pb in galena, PbS. Thallium(I) has a similar radius to Rb and so also concentrates with this element in the late magmatic potassium minerals such as feldspars and micas. 

D, 8 0 and Cl concentration data suggest the mixing of meteoric water, connate seawater and magmatic gas (Seki, 1991) (Fig. 2.20). Br/Cl and B/Cl ratios are different from those of seawater (Fig. 2.21). This difference and N2-H2-Ar gas composition indicate a contribution of magmatic gas (Seki, 1991, 1996). 

In magmatic processes, both parent and daughter nuclides are usually present in the solid sources, magmas and crystallizing minerals, so that (N2), which is a priori unknown, cannot be neglected. In order to solve Equation (I) for t, the age of fractionation, both terms of this equation are divided by the concentration of a stable isotope (or the activity of a long-lived isotope) of the daughter element. Such a normalization, similar to those used in other classical radiometric methods (Rb-Sr, Sm-... 

There is no evidence that the depth may be a result of an alteration in the original concentration of magmatic sulphides. It may be a result of concentration of hydrothermal solutions. 

Figure 3.3 Schematic residual magma-cumulate relationships for instantaneous and average magmatic products in a linear plot of Ni and Cr concentrations. For mass balance to be obeyed, the instantaneous cumulate must lie on the tangent to the liquid line of descent at the point representing the instantaneous liquid.

Molybdenite is the only common concentrator and economic source of Re. This is because MoS2-ReS2 effectively comprises a solid solution. The association of Re with Mo in this manner suggests that Mo and Re may also behave similarly during magmatic processes. 

Rhenium abundance in most rocks is measured in parts per billion or less and minerals in which it is a major constituent are rare. It is similar geochemically to molybdenum, which it commonly accompanies through magmatic and related hydrothermal stages, and is concentrated in molybdenite associated with various types of granite-related deposits. Molybdenites with some of the highest concentrations of rhenium are associated with porphyry Cu and Cu-Au deposits, which are the primary industrial source of rhenium. Rhenium can also be concentrated by low-temperature... 

Relatively recently, AIS Sommer GmbH of Germany delivered a laser-induced fluorescence (LIP) analyzer for quality control in minerals and mineral processing (Broicher 2000). The LIP analyzer includes two light detector systems with three photomultipliers each, which evaluate three spectral bands in two time windows each. It was done in the Kiruna phosphorous iron ore mine, Sweden. The limitation of LIP analysis is that its accuracy depends on the complexity of the composition of the ore and the concentration and fluorescence properties of the critical minerals in relation to all the other minerals present. The phosphorous iron ore in Kiruna is ideal for LIP analyzes, because its iron minerals are practically non-luminescent, while magmatic apatite is strongly fluorescent with intensive emissions of Ce and Eu ". ... 

The study of the basaltic dykes in evaporites demonstrates that dissolution and precipitation of phosphate minerals is a key process for the control of REE mobility and REE fractionation. In the present case, all REE found in secondary apatite in the basalt and in the salt are derived from the dissolution of primary magmatic apatite during basalt corrosion. This loss of REE from the basalt to the salt was not sufficient to lower significantly the REE concentrations of the basalt and it could only be detected by the analysis of the salt. The absolute quantity of REE transferred from the basalt into the salt, however, cannot be quantified because we have no three-dimensional control on the REE concentrations around the basalt apophy sis. 

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