Hypogene minerals

In the leach cap, the Cu isotopes are lighter than those in the enrichment blanket. Near the surface, the isotopes are extremely low, to about -14%o. Deeper in vertical profile at about 300 feet, the enrichment blanket contains a heavier isotope signature around 8%o. This pattern is observed throughout the drill core. The hypogene mineralization is near 0%o and therefore, there has been fractionation of copper isotopes in the chalcopyrite during dissolution. This fractionation is seen because the hypogene ores are distinctly different than leach cap and enrichment minerals. 

Various forms of dead organic matter, fragments of durable hypogenic minerals, and numerous products of biogeochemical and geochemical transformations and weathering represent the non-living part of soil. 

Third, the restriction associated with the mass action law was rmtil now used without consideration of kinetics as it was applied only to sufficiently fast reactions. However, in the interaction between water and rock participate reactions of various kinetics. Whereas the relaxation of homogeneous processes in water completes in hours or minutes, it is between water and rock, especially silicate ones, may last for years and decades. Simultaneously, in conditions of lowered temperature hypogene minerals only dissolve, hypergene ones dissolve or form, and the ground water composition continuously maintains thermodynamical equilibrium. In order to account for such kinetic variety of the mass transfer processes, they are tentatively subdivided into two groups reactions of irreversible mass transfer and reactions of instantaneous relaxation. 

This imaginary experiment shows that the more fresh water per imit weight of hypogene minerals, the more significant is their transformation into secondary aluminum silicates. Thus, one and the same hypogene mineral, for instance albite, can convert into montmorillonite, kaolinite or even gibbsite. With small volume of water and low content, in aliuninum silicate almost entire (89%) silicon is preserved, and mostly montmorillonites form ... 

Table 2.25 Average longevity of hypogene minerals at 25 C and pH 5 (Lasaga, 1984).

The polymetallic veins are poorly exposed at surface and are characterized by the presence of gossans with remnants of breccias with quartz matrix and oxidized sulfide clasts. Hypogene polymetallic mineralization is characterized by the presence of massive and banded sulfide veins and sulfide breccias up to 13 m thick. This mineralization is developed In... 

Case-1 Porphyry-type Cu assays and mineral abundances were measured at 3 meter intervals through a Cu-Au porphyry. Figure 1 displays the sample depth vs. the total clay content vs. the Cu-Sulfide content (chalcopyrite and secondary Cu-sulfides such as bornite and covellite). Based on the mineral abundances, three distinct zones are recognized leached, supergene and hypogene zones, each... 

Fig. 1. An example of a Cu-Porphyry defining the leached, supergene and hypogene enriched zone from the mineral abundances of a typical figure.

Fig. 3.39 5D and values for kaolonites and related minerals from weathering and hydrothermal environments. The Meteoric Water Line, kaohnite weathering and su-pergene/hypogene (S/H) lines are given for reference (after Sheppard and Gilg 1995)... 

Brimhall G. H. (1979) Lithologic determination of mass transfer mechanisms of multiple-stage porphyry copper mineralization at Butte, Montana vein formation by hypogene leaching and enrichment of potassium silicate protore. Econ. Geol. 74, 556-589. 

The rationale for using Hg as a pathfinder element in mineral exploration is attractive. Because of its volatility, Hg is presumed to form broader halos in the hypogene environment than most elements. It is envisaged that both vapour-phase and solution transport are responsible for a wide dispersion of the element. In the secondary environment it is well known that Hg exerts a measurable vapour pressure at ambient temperatures and possesses redox properties that allow the metal to exist in the elemental state under a range of natural conditions. Therefore it has been claimed that, as a host sulphide-body weathers, it can be expected that Hg will be converted partly to the vapour state, thereby overcoming the constraint of hydromorphic or solution dispersion that applies to other target and indicator elements. Vapour-phase dispersion through permeable rock or cover would allow Hg to be detected in soil or soil gas, and perhaps as an atmospheric anomaly. 

Recent studies showed that hydrolytic leaching is dissolution of the primary mineral and the precipitation on its surface of the secondary one. At that, part of H O dipoles passes into the composition of mineral forming so called constitution water, and the solution is enriched in orthosilicic acid and metals, mostly alkali and alkali earth ones (first of all Na, K and Ca). In the process, hypogene rock-forming minerals convert into clay, oxides and hydroxides. Newly-formed hypergene minerals turn out even less soluble and more stable in humid medium of low temperature and pressure. A number of such reactions of hydrolytic substitution of the primary silicate minerals by clay ones are represented below ... 

As hypogene relic minerals in this case are meant those, which at mass transfer with water in conditions of relatively low temperature only destruct, dissolve and do not form. These minerals are represented mostly by aluminum silicates of igneous, metamorphic and clastic sedimentary... 

Thus, the entire path of relaxation for the system water-rock up to total equilibrium may be presented as some distance and the process itself as moving along this distance. At that, the distance passed maybe expressed either in fractions of unit as part o the distance or in imits of time At, if the process rate is known. For hypergene secondary minerals, this time is often disregarded. But between most hypogene primary minerals, especially aluminum silicates and silicates, the mass transfer with water is irreversible and has the lowermost rates. 

Chemical weathering is least effective with minerals of hypogene rocks (quartz, feldspars, micas, etc.). Their dissolution is very slow and is accompanied by the formation of secondary, even less soluble hypergene minerals (clay, gibbsite, boehmite, limonite, etc.). The rate of such substitution depends on intensity of water-exchange with the surface and aggressiveness... 

Thus, the transformation extent of hypogene rocks depends first of all on the abundance and acidity of water. The more intense the water-exchange and the lower pH value in water, the greater the amount of silicon is removed, and the faster and deeper is the process of chemical weathering. In the localities of more alkaline water from hypogene rock-forming minerals form mostly montmorillonites, wherever neutral weakly-acidic water dominates, form kaolinites, and in the areas of abimdant acid water - gibbsite. 

Table 1. Amount of hypogene and hypergene minerals in the modeled systems of tailings oxidation in contact with the host rock. 

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