Minerals veins

A Galenite (PbS2) in mineral veins is very conspicuous, which led to the early discovery of the metal. 

Mobile, on-line XRF methods have been tested in the Au exploration targets. Analysis of continuous till and weathered bedrock samples shows clear variation of the contents of pathfinder elements of hydrothermal alteration. Particularly, in the weathered bedrock, the presence of narrow mineralized veins is seen (Fig. 5). One interesting feature is that the indication of the weathered bedrock sources can be traced 2 to 5 m down-ice in the till. These results suggest very short glacial transport of mineralized debris from the bedrock sources. Information on... 

Fig. 2. EPMA back-scattered electron images of a polished section from Chelehkureh deposit, a) carbonate in a mineralized vein with chalcopyrite b) larger image of carbonate grain marked by + in previous image, c), d) and e) are in turn compositional Mg, Fe and Ca images of that grain.

Mineral chemistry of carbonates of mineralized veins in the Chehelkureh ore deposit show that at least some of these carbonates were deposited from hydrothermal fluids of igneous origin, which is consistent with carbon isotopes results (Maanijou 2007). 

The presence of pyrites in mineral veins is frequently betrayed by the brown, rusty appearance of the upper parts of the deposits. This is well exemplified in the case of certain copper lodes, the iron of the contained copper pyrites having become converted into hydrated ferric oxide or rust. Such weathered zones are known as gozzans, and frequently present a cavernous or honeycombed appearance, due to the removal of pyritic material. In France the gozzan is termed the chapeau de fer, and in Germany der eiserne Hut, and an old adage states that4... 

Pegmatite coarse-grained mineral vein with well formed... 

PameU J., Honghan C., Middleton D., Haggan T., and Carey P. (2000) Significance of fibrous mineral veins in hydrocarbon migration fluid inclusion studies. J. Chem. Explor. 69-70, 623-627. 

All fractures generated by internal fluid overpressure are here referred to as hydrofractures. The fracture-generating fluid may be oil, gas, magma, groundwater, or geothermal water. Hydrofractures include dykes, inclined sheets, mineral veins, many joints, and the man-made hydraulic fractures that are used in the petroleum industry to increase the permeability of reservoir rocks. Hydrofractures are primarily extension fractures (Gudmundsson et al. 2001). The difference between the total fluid pressure in a hydrofracture and the normal stress, which for extension fractures is the minimum compressive principal stress, oj, is referred to as the fluid overpressure. 

In this paper we present field examples of hydrofractures as mineral veins in layered sedimentary rocks and compare these observations with numerical models. We investigate the propagation of hydrofractures and then use analytical models based on field measurements to estimate the fluid overpressure and depth to the fluid sources of the veins. We also explore the effects of layering on aperture variations of such hydrofractures. 

Most mineral veins in the damage zones, however, are restricted to the limestone layers, that is, are stratabound extension fractures (Fig. 2). This means that the permeability was less than it would have been in case the veins propagated through many layers. 

To obtain the fluid overpressure of the hydrofractures that formed the mineral veins in the field area at the Somerset Coast (Figs 1 and 2), we measured the length and aperture (thickness) of 239 calcite veins exposed in subhorizontal limestone layers. We used only veins that have both ends visible in the outcrop, are continuous, and are non-restrictive (that is not dissecting other veins or other discontinuities). All the measured veins are extension fractures that show no evidence of subsequent shear deformation. 

Mineral veins rich in bastnaesite have been found in mines in Weishan (Shandung) and in Mianning (Sichuan). These deposits give ores from which the rare earths are much easier to separate than from the Baiyunebo mixed minerals, favoring high yield... 

Mineralization occurs (a) in east-west veinlets and veins varying from a few centimetres to a few metres in width they occur together between levels 80 and 40 m and beyond up to the surface, forming a locally very rich stockwork, and (6) in the fractures of the filon-toit -BN6 and filon-mur systems, where mineralized veins show thicknesses from several metres to a few tens of metres carrying sooty pitchblende, hexavalent uranium minerals in a jasper and banded quartz gangue. 

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