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In situ gold-bearing vein (in brown) at the Toi gold mine, Japan. In many gold mines exploited during the gold rushes of the 19th century, vein material alone was typically sought as ore material. [8] In most of today's mines, ore material is primarily composed of the veins and some component of the wall rocks which surrounds the veins. [9]
Along an ore shoot, there is a rich gathering of different minerals within a vein. The veins can resemble a pipe, chimney or ribbon in structure and are displaced mainly vertically oriented but also can be horizontal with large veins extending approximately 30 m (100 ft) horizontally and 150 m (500 ft) vertically. [3]
IOCG deposits typically occur at the margins of large igneous bodies which intrude into sedimentary strata. As such, IOCG deposits form pipe-like, mantle-like or extensive breccia-vein sheets within the host stratigraphy. Morphology is often not an important criterion of the ore body itself, and is determined by the host stratigraphy and ...
Quartz is generally the dominant mineral in the veins, but there are also gold bearing carbonate dominant veins in orogenic deposits. [15] Ore bodies of orogenic gold deposits are generally defined by ≤ 3–5% sulfide minerals, most commonly arsenopyrite in metasedimentary host rocks and pyrite/pyrrhotite in meta-igneous rocks, and ≤ 5–15 ...
Hydrothermal vein ore deposits consist of discrete veins or groups of closely spaced veins. Veins are believed to be precipitated by hydrothermal solutions travelling along discontinuities in a rockmass. [10] They are commonly epithermal in origin, that is to say they form at relatively high crustal levels and moderate to low temperatures.
When the ore forms a blanketlike body along the bedding plane of the rock, it is commonly called a manto ore deposit. Other ore geometries are chimneys and veins. [ 4 ] Polymetallic replacements/mantos are often stratiform wall-rock replacement orebodies distal to porphyry copper deposits, [ 5 ] or porphyry molybdenum deposits. [ 6 ]
Unlike most silver ore deposits, which occur in long thin veins, those of the Comstock Lode occurred in discrete masses often hundreds of feet thick. Sometimes, the ore was so soft it could be removed by shovel. Although this allowed the ore to be easily excavated, the weakness of the surrounding rock resulted in frequent and deadly cave-ins.
The ore deposit at Kiruna is part of a larger iron ore province stretching west-east from Kiruna to the Finnish border. [6] This province includes thus also the ores at Svappavaara and Pajala. [6] Malmberget is a large notable southward outlier of this province. [6]