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The Tin Mountain pegmatite is an igneous intrusion located in the southern Black Hills, South Dakota. It is a part of the Harney Peak Granite dome that formed in the Late Paleoproterozoic around 1.7 billion years ago. [ 1 ][ 2 ][ 3 ] The Harney Peak Granite system includes thousands of pegmatites, one of which is the Tin Mountain. [ 1 ]
Pegmatite. A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than 1 cm (0.4 in) and sometimes greater than 1 meter (3 ft). Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic composition to granite.
Pikes Peak granite is a 1.08 billion year old Late-Precambrian geologic formation found in the central part of the Front Range of Colorado. It is a coarse-grained pink to light red syenogranite with minor gray monzogranite , and it has a distinctive brick-red appearance where it outcrops.
Since fine-grained granite is less porous, this "outer skin" sealed the magma body and helped to trap rare elements and water inside. Over time, the water and rare elements were concentrated along the edges of the magma. While the magma cooled and crystallized, the water content of the remaining liquid magma increased rapidly.
These igneous intrusive rocks consist of granitic and pegmatitic dike swarms, i.e. the Cottonwood, Cremation, Sapphire, and Garnet pegmatite complexes, that cut the Granite Gorge Metamorphic Suite from east to west. They formed as granite magma, and related pegmatite fluids, filled crack-systems as magma migrated through the crust. The chemical ...
Granite often occurs as relatively small, less than 100 km 2 stock masses and in batholiths that are often associated with orogenic mountain ranges. Small dikes of granitic composition called aplites are often associated with the margins of granitic intrusions. In some locations, very coarse-grained pegmatite masses occur with granite. [18]
Greisen is formed by self-generated alteration of a granite and is a class of moderate- to high-temperature magmatic-hydrothermal alteration related to the late-stage release of volatiles dissolved in a magma during the solidification of that magma. Greisens are usually variably altered rocks, grading from coarse, crystalline granite, commonly ...
Granite and granite pegmatite (2545 ± 30 Ma) intrude metasedimentary rock of the Miners Delight Formation in the western part of the greenstone belt. The South Pass pluton is a pegmatitic granite west of South Pass City, and the Sweetwater granite is a fine-to medium-grained leucocratic granite that occurs to the west of the South Pass pluton along the Sweetwater River and Lander Creek.