What is metamorphic devolatilization?

Abstract. A metamorphic devolatilization model can explain the enrichment, segregation, timing, distribution and character of many goldfields such as those found in Archean greenstone belts, slate-belts and other gold-only provinces.

How is gold deposits formed?

Gold may occur as deposits called lodes, or veins, in fractured rock. It may also be dispersed within Earth’s crust. Most lode deposits form when heated fluids circulate through gold-bearing rocks, picking up gold and concentrating it in new locations in the crust.

Does gold form in metamorphic rocks?

In metamorphic rocks the range of gold content is from 0.86 to 22.4 ppb with an average of 4. 3. The average (in parts per billion) for gneiss is 1.8; for schist, 5.0; for quartzite, 4.8; and for mar- ble, 3.1.

What is the geologic structure of gold?

Gold mineralization is associated with sulphide mineral assemblages dominated mainly by pyrite, pyrrhotite and chalcopyrite. Gold is present both as free Au in wall rock and in association with pyrite.

How are metamorphic deposits formed?

Metamorphic rocks are formed from heat and fluids near cooling magma (contact metamorphism) and by high temperatures and pressures deep with the crust (regional metamorphism). Although rock metamorphism certainly plays an important role in ore deposition, most of the resulting deposits are classified as hydrothermal.

Is gold metamorphic?

According to Large et al. (2011), most of orogenic gold deposits across the globe are commonly associated with processes of metamorphism, usually with the formation of the ore-minerals in terranes of low metamorphic grade.

How many types of gold deposits are there?

orogenic gold deposits 2. Carlin-type gold deposits 3. epithermal deposits 4. porphyry copper-gold deposits 5.

How are secondary gold deposits formed?

Secondary Gold Deposits The gold is flushed out of the rock and accumulates with other heavy minerals as fine gold dust or as small grains, the so-called “nuggets”, in the shallows of streams and rivers. The so-called “placer gold” is formed.

Where are gold deposits found?

California Placer Deposits Streams draining the rich Mother Lode region–the Feather, Mokelumne, American, Cosumnes, Calaveras, and Yuba Rivers–and the Trinity River in northern California have concentrated considerable quantities of gold in gravels.

What rocks are associated with gold?

The ore minerals associated with gold consist of base metal sulphides and Sb-bearing suphosalts. Arsenopyrite, pyrite, chalcopyrite, sphalerite, pyrrho- tite and galena are the principal sulphide minerals present. The sulphosalts include tetrahedrite, boulan- gerite, bournonite and jamesonite.

Where are gold deposits?

Gold is usually found embedded in quartz veins, or placer stream gravel. It is mined in South Africa, the USA (Nevada, Alaska), Russia, Australia and Canada.

What is metamorphic deposit?

An ore deposit that has been subjected to great pressure, high temperature, and alteration by solutions. It may have become warped, twisted, or folded, and the original minerals may have been rearranged and recrystallized.