What is a Copper Porphyry?
Changing the Game - If Silver Bullet Mines has a Copper Porphyry on the Property, it can be worth $Billions
From Wikipedia, the free encyclopedia
Porphyry copper deposits are copper ore bodies that are formed from hydrothermal fluids that originate from a voluminous magma chamber several kilometers below the deposit itself. Predating or associated with those fluids are vertical dikes of porphyritic intrusive rocks from which this deposit type derives its name. In later stages, circulating meteoric fluids may interact with the magmatic fluids. Successive envelopes of hydrothermal alteration typically enclose a core of disseminated ore minerals in often stockwork-forming hairline fractures and veins. Because of their large volume, porphyry orebodies can be economic from copper concentrations as low as 0.15% copper and can have economic amounts of by-products such as molybdenum, silver, and gold. In some mines, those metals are the main product.
The first mining of low-grade copper porphyry deposits from large open pits coincided roughly with the introduction of steam shovels, the construction of railroads, and a surge in market demand near the start of the 20th century. Some mines exploit porphyry deposits that contain sufficient gold or molybdenum, but little or no copper.
Porphyry copper deposits are currently the largest source of copper ore. Most of the known porphyrys are concentrated in: western South and North America and Southeast Asia and Oceania - along the Pacific Ring of Fire; the Caribbean; southern central Europe and the area around eastern Turkey; scattered areas in China, the Mideast, Russia, and the CIS states; and eastern Australia. Only a few are identified in Africa, in Namibia and Zambia; none are known in Antarctica. The greatest concentration of the largest copper porphyrys is in northern Chile. Almost all mines exploiting large porphyry deposits produce from open pits.
Geological background and economic significance
Porphyry copper deposits represent an important resource and the dominant source of copper that is mined today to satisfy global demand. Via compilation of geological data, it has been found that the majority of porphyry deposits are Phanerozoic in age and were emplaced at depths of approximately 1 to 6 kilometres with vertical thicknesses on average of 2 kilometres. Throughout the Phanerozoic an estimated 125,895 porphyry copper deposits were formed; however, 62% of them (78,106) have been removed by uplift and erosion. Thus, 38% (47,789) remain in the crust, of which there are 574 known deposits that are at the surface. It is estimated that the Earth's porphyry copper deposits contain approximately 1.7×1011 tonnes of copper, equivalent to more than 8,000 years of global mine production.
Porphyry deposits represent an important resource of copper; however, they are also important sources of gold and molybdenum - with porphyry deposits being the dominant source of the latter. In general, porphyry deposits are characterized by low grades of ore mineralization, a porphyritic intrusive complex that is surrounded by a vein stockwork and hydrothermal breccias. Porphyry deposits are formed in arc-related settings and are associated with subduction zone magmas. Porphyry deposits are clustered in discrete mineral provinces, which implies that there is some form of geodynamic control or crustal influence affecting the location of porphyry formation. Porphyry deposits tend to occur in linear, orogen-parallel belts (such as the Andes in South America).