Tonalites grade into granodiorites with increase in alkali feldspar content. Some authors refer to leucocratic tonalite or granodiorite containing very little or no alkali feldspar as trondhjemite.
Feldspathoid-bearing variants occur, but are comparatively rare. With more calcic plagioclase, diorites grade into gabbros. Skip to main content Skip to table of contents. This service is more advanced with JavaScript available. Petrology Edition. Contents Search. Diorite and tonalite. Authors Authors and affiliations Ian Parsons. How to cite. The second, lower temperature stage gave a polyphase gold-rich mineralization that developed in four phases which are distinguished by different parageneses including:.
Phase 1. Phase 2. Chlorite, epidote, calcite, gold, native Bi , Bi-Pb sulfides , galena, chalcopyrite , fahlore , pyrite , Fe-gersdorffite. Phase 3. The gold mineralization is exclusively associated with phase 2 and developed in three sulfide parageneses:. The hydrothermal alteration and mineralization formed after the consolidation of the Rebecca diorite and Bindura granodiorite, most probably in the postmagmatic cooling stage.
The mineralization was emplaced either synchronously or subsequently to the shear zones which crosscut the consolidated pluton. Not all shear zones are mineralized and different shear zones show different amounts of mineralization and hydrothermal alteration.
It cannot be excluded that this process developed in a plutonic porphyry copper-like environment, in which the classically hydrothermal zonation did not form due to synchronous tectonic disturbance, which preferentially drives the hydrothermal flow along shear zones.
This is a preview of subscription content, access via your institution. Rent this article via DeepDyve. You can also search for this author in PubMed Google Scholar. Dolerite is an igneous rock , that is, rock initially molten and injected as a fluid into older sedimentary rocks.
The magma, of quartz tholeiite composition, was emplaced as a liquid which rose upwards through the basement rocks into older sedimentary rocks of the Parmeener Supergroup. Chalk forms from a fine-grained marine sediment known as ooze.
When foraminifera, marine algae, or other organisms living on the bottom or in the waters above die, their remains sink to the bottom and accumulate as ooze. Extensive deposits of chalk are found in many parts of the world. Chalk Characteristics and Properties Chalk, in both its natural and man-made form , is white in colour and is considered to be a fairly soft solid. Naturally, It comes from the ground where it is found as a porous can hold water sedimentary rock. It is a form of limestone and is composed of the mineral calcite.
Chalk, soft, fine-grained, easily pulverized, white-to-grayish variety of limestone. Chalk is composed of the shells of such minute marine organisms as foraminifera, coccoliths, and rhabdoliths. The purest varieties contain up to 99 percent calcium carbonate in the form of the mineral calcite.
Granite is an intrusive igneous rock. Intrusive rocks form from molten material magma that flows and solidifies underground, where magma cools slowly. Extrusive igneous rocks erupt onto the surface, where they cool quickly to form small crystals. Some cool so quickly that they form an amorphous glass. These rocks include: andesite, basalt, dacite, obsidian, pumice, rhyolite, scoria, and tuff.
Although referred to as marble, the rock is of purely sedimentary origin. It is a dark, fine-grained, muddy Carboniferous limestone, rich in bitumen which gives it its dark grey colouration which turns a glossy black when polished and surface treated.
Cultured marble is a man-made surface , while marble is natural from the earth. Marble has a more luxurious look and feel and costs more. Are granodiorite intrusive or extrusive? Asked by: Mrs. Francesca Gorczany PhD.
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