Mining in Manitoba |
Primary Mineral Deposits |
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Mineral deposits formed from magmas are called Primary Mineral Deposits and are subdivided into : Syngenetic Deposits (formed at the same time as the country rock and is enclosed by it) Epigenetic Deposits (formed in a parent rock by a mother liquor penetrating into surrounding rocks) Primary mineral deposits are eventually subjected to alterations through weathering, both chemical and mechanical, and give rise to Secondary Deposits.
SYNGENETIC DEPOSITS There are 2 types of syngenetic deposits, the igneous and the sedimentary. Syngenetic deposits or magmatic segregations are formed by the solidification of basic magmatic material and occur as dykes and irregular masses. The deposits are associated with characteristic igneous parent rocks that are fresh or are slightly altered. Syngenetic Sedimentary Deposits include placer deposits and beds, which are simple sedimentary rocks containing valuable minerals to be called ore.
EPIGENETIC DEPOSITS Most mining areas containing Epigenetic deposits are commonly characterized by the presence of intrusive igneous rocks, by complex folding and deformation of the geologic structure, and by alteration of the country rock through the action of circulating mineral solutions. These deposits can be classified into 6 types: 1) Contact Metamorphism These are formed in the zone next to a magma with soluble or replaceable rocks. Magma gases and solutions invade and change the rocks which they intrude, forming new minerals and depositing valuable metals. 2) Pegmatite Deposits Found in or near igneous rocks and at the outer margins of intrusive masses. 3) Deep-seated Veins It is estimated that these deposits were formed at depths of >12,000 ft. beneath the earth's surface and at 300-575 C temperature. The mineralizing solutions entered fissures and other openings under great pressure. The deposits are commonly tabular or veinlike in form. 4) Intermediate Veins These deposits formed at depths ranging from 4000 to 12000 ft. below the surface and at a temperature between 175-300C. Such a deposit may take the form of a fissure vein, or a series of parallel fissures called a sheeted zone, of a replacement of the wall rock of fissures, or of a large disseminated deposit. 5) Shallow Veins Formed at depths probably not greater than 2000 ft below the surface and within a temperature of 50 to 200C. They are found as tabular veins, irregular veins with ore chambers, and as ledges and irregular displacement deposits. 6) Surface deposits by springs These minor deposits of metal are of little economic importance. |
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