Metamorphic deposits

Scapolite is found in the metamoiphic locks, particularly those, rich in calcium also in contact metamorphic deposits in limestones. It has been found in basic igneous rocks, probably as a secondary mineral. Notable localities are Lake Baikal, Siberia Arendal. Norway and Madagascar. In the United States, it is found in Massachusetts, New York, and New Jersey. Greenville, in the Province of Quebec, Canada is an important locality. Superb transparent yellow gem crystals have recently been found in Brazil and Tanzania. Wernente (scapolite) was named in honor of A.O. Werner, a famous German mineralogist (1749-1817). 

The rock mass movement of magmatic and metamorphic deposits tends to be under the master control of horizontal tectonic principal stress (Zhao et al. 2012b). This rule was proved by the in-situ stress measurement conducted by Miao et al. (2004) in the Sanshandao mine. The stress values were calculated from the strain values, rock elastic modulus and Poisson ratios of four measurement points installed separately in the south section of -75 m drift, north section of -150 m drift and south and north of -420 m. For both the Xinli mine and the Sanshandao mine belong to a same ore-controlling fault belt, their in-situ... 

Rossing is the largest known anatectic or ultra-metamorphic deposit, containing about 150 000 ton UsOs at an average grade of 0.035% U3O8. 

Sources. Iron ore deposits were formed by many different processes, eg, weathering, sedimentation, hydrothermal, and chemical. Iron ores occur in igneous, metamorphic, and sedimentary deposits. Normally, as-mined iron ore contains 25 to 68% iron. 

The Utah deposit is located in southwestern Utah near Cedar City. The iron ore deposits are of contact metamorphic origin. The cmde ore contains 35 to 65% iron, primarily in the form of magnetite and goethite. Mining is done by the open pit method. The cmde ore is cmshed, screened at —75 mm (—200 mesh size) and shipped as lump ore containing 54% iron. The ore is rescreened at the steel mill to produce lump ore (10—64 mm) for the blast furnace and sinter feed (0—10 mm) for the sinter plant. 

Quartz-Pebble Conglomerate Deposits. Known quartz-pebble conglomerate ores are restricted to a specific period of geologic time. These ore types occur in basal Lower Proterozoic beds unconformably situated above Archaean basement rocks composed of granitic and metamorphic strata. A number of commercial deposits are located in Canada and South Africa. Some subeconomic occurrences have been reported in Brazil and India... 

MetamorphicDeposits. Uranium deposits belonging to the metamorphic class occur in metasediments or metavolcanics generally, without direct evidence of post-metamorphic mineralization. Examples include the deposits at Eorstau, Austria (16). 

Talc of metasedimentary origin is formed by hydrothermal alteration of a dolomitic host rock by a silica-containing fluid. This type of deposit is typical of Montana and AustraUa. It is usually quite pure with talc content of 90 to 98% and often very white as well. Dolomite [17069-72-6], CaMg(C02)2, is the most common accessory mineral. The fourth type is of metamorphic origin, where a siUcaceous dolostone is first converted to tremolite [14567-73-8] or actinohte [13768-00-8] and then partially converted to talc. The Balmat, New York, and Death Valley, California, deposits are of this type. Tremolite, dolomite, and serpentine are common accessory minerals. This type of talc deposit has a variable talc content (30—80%), but is usually white and often commercially exploited because of the properties of its accessory minerals rather than the talc. 

Tungsten deposits occur in association with metamorphic rocks and granitic igneous rocks throughout the world (Table 2). Deposits in China constitute over half of the world reserves and over five times the reserves of the second largest source, Canada. 

Barite [13462-86-7], natural barium sulfate, BaSO, commonly known as barytes, and sometimes as heavy spar, tiU, or cawk, occurs in many geological environments in sedimentary, igneous, and metamorphic rocks. Commercial deposits are of three types vein and cavity filling deposits residual deposits and bedded deposits. Most commercial sources are replacement deposits in limestone, dolomitic sandstone, and shales, or residual deposits caused by differential weathering that result in lumps of barite enclosed in clay. Barite is widely distributed and has minable deposits in many countries. 

Figure 1.62. Location of epithermal-type deposits in Japan (Shikazono and Shimizu, 1988a). 1 Green tuff and subaerial volcanic region of Tertiary/Quaternary ages, 2 Main Paleozoic/Mesozoic sedimentary terranes, 3 Main metamorphic terranes. TTL Tanakura tectonic line, ISTL Itoigawa-Shizuoka tectonic line, MTL Median tectonic line. Open circle epithermal Au-Ag vein-type deposits, solid circle epithermal base metal vein-type deposits, open triangle epithermal Au disseminated-type deposits.

The Tsugu gold-antimony deposit is located in the central part of Honshu, Japan (Fig. 1.171). Geologically, the Tsugu deposit occurs in the Ryoke metamorphic terrane. 

The deposits occurring in the sedimentary rocks (mainly black shale) are distributed mainly in three districts Kitakami, Yamizo and Koma (Fig. 1.185). The few deposits in the metamorphic region are the Suwa, Kinkei, Amo and Hashidate (Fig. 1.185). 

Figure I.I92. Frequency (no. of analy.ses) histograms for Ag content (in atomic %) of gold from hypo/ mesothermal gold vein-type deposits in Japan. K Kuryu deposit, Sh Shiozawa deposit, D Daigo deposit, Sa Saigane deposit. Data are from the Yamizo Mountains Shikazono and Shimizu (1988a) the South Koma Region Shikazono and Shimizu (1987) the Kitakami Mountains Nedachi (1974) Yamaoka (1981), Abe (1981) and Shikazono and Shimizu (1987) metamorphic regions Shikazono and Shimizu (1987).

Kojima et al. (1956) found that most of the Besshi-subtype deposits in the Sanbagawa metamorphic terrain of Shikoku occur in the Minawa Formation characterized by the basic schists, metamorphic equivalents of basaltic lavas and hyaloclastics, based on the summary of the stratigraphic horizon of about one hundred Besshi-subtype deposits. 

Besshi-type deposits in Sanbagawa metamorphic terrain occur in the Minawa Formation which is composed of basic schist. Sometimes, they are associated with quartz schists. Probably, quartz has been originally formed from hydrothermal solution like siliceous ore in Kuroko deposits. Original rocks of basic schists are basaltic lava and hyaloclastics. Detailed geochemical investigation on the basic schists in the Sanbagawa... 

Kase and Horiuchi (1996) obtained a large number of analytical data on sphalerites from sixteen Besshi-type deposits, mainly at Besshi and its vicinity, Hitachi, and Shimokawa. They revealed that (1) the Mn/Zn and Co/Zn ratios of sphalerite may have markedly increased during contact metamorphism, while the Cd/Zn ratios remained unchanged (2) the Emco/ lwzn (2/n total dissolved concentration in ore fluids) and Emco/S/wzn ratios in the initial ore solutions responsible for the mineralizations at Besshi which was calculated ba.sed on the equilibrium fractionation model between hydrothermal solution and sphalerite and analytical data on sphalerites are quite similar to the ratios of hydrothermal solutions at EPR 21 °N (3) however, these ratios for the Hitachi solutions are very low and different from those of the Besshi-subtype solution. 

Galena, tetrahedrite-tennantite, mawsonite and native silver occur in the copper rich ores but not in ordinary pyritic ores and copper rich ores most commonly occur as offshoots, tongues and veins in the deformed deposits. This suggests that these minor minerals formed during the metamorphic deformation stage accompanied by recrystallization. 

The geochemical environment of ore deposition for Besshi-type deposits is generally difficult to estimate because of the effect of metamorphism. 

Doi, M. (1961-1962) Geology and cupriferous pyrite deposits (Besshi-type) of the Sanbagawa metamorphic zone including the Besshi and Sazare mines in central Shikoku. Mining Geology, II, 610-626 12, 1-15, 6.3-83. 

Kase, K. (1972) Metamorphism and mineral assemblages of ores from cupriferous iron sulfide deposit of the Besshi mine, central Shikoku, Japan. J. Fac. Set U. Tokyo, Sec. 2, 18, 301-323. 

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