Magmatic and Non-Magmatic Ores

It is of importance, in prospecting, to distinguish ores of magmatic origin from those derived by the metamorphism and granitization of source rocks and from those accumulated in certain sedimentary facies. The magmatic ores, which are characterized by their occurrence along fault structures, may be associated with volcanic (including explosive) phenomena. Heat effects are local. The magmatic sequence is well defined: kimberlite, with diamond pipes; ijolite, with carbonatites; peridotite, with nickel deposits; norite, with nickel-copper deposits; and diabase- gabbro, with copper-zinc deposits. These deposits are characteristic of Precambrian shields, where a thick sialic crust may rest on basic to ultrabasic magma. The sequence is resumed in the Paleozoic terrains (in a broad sense), with monzonite porphyries and associated copper, copper-gold, and copper- lead-zinc deposits. The monzonite and andesite intrusives, with associated copper and copper- lead-zinc deposits, extend into the Mesozoic and Tertiary belts, where they have their greatest development. In some cases, as at Braden, .Chile, the ores are found in actual explosive volcanic centres. The development of the gold-silver telluride ores, the mercury ores, and the hot springs, with accompanying sulphur deposition, has taken place in Tertiary to Recent rocks, usually along lines of crustal weakness. The above sequence represents decreasing depth, decreasing time and decreasing temperature, and conforms to Lindgren's temperature-depth classification. However, the granitic rocks, including paragneisses, do not fit into the magmatic sequence, and may be of metamorphic origin. The numerous non-magmatic metalliferous provinces generally have little to do with crustal weakness, "main breaks," etc. In prospecting, the same thinking that is applicable to magmattic ores may be quite misleading when dealing with non-magmatic deposits. As an example, the ores associated with carbonate-rich shelf sediments are discussed in a section of this paper
Keywords: copper, copper, igneous, peridotite, Precambrian, specific gravity, Deposits, Ore, Ores, Rock, Rocks, Volcanic
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