Proses-proses Geologi

Berikut ini yaitu proses-proses yang mengkonsentrasikan logam dengan endapan mineral 1. Proses ortomagmatik Proses ini yaitu meliputi pembentuk batuan beku dan bijih. A number of mineral deposits have formed by magmatic, segregation processes; they are often called orthomagmatic deposits. These Deposits are important sources of chromium, titanium, vanadium, the platinum group metals, copper, nickel (and diamonds). Much titanium, diamond and significant amounts of the platinum group metals are mined from sedimentary placer deposits, formed by the weathering of these primary deposits. (Wilson (ed.), 1969) 2. Proses pasca magmatik Metasomatism: Fuids rich in dissolved ions may migrate into adjacent rocks, causing reactions that change the rock's bulk composition. Common examples of this are seen in metamorphic rocks that are cris-crossed by veins of quartz. This quartz originated as silica dissolved in pore fluid precipitated inside fractures. The silica originated in the surrounding rock but migrated out with pore fluid during metamorphism. Note: Metasomitism is an important process by which deposits of metals and metal ores are formed. a. Pirometasomatik b. Pegmatitik c. Hidrotermal hipogen (epitermal, mesotermal, hipotermal) 3. Proses pelapukan Terdiri dari proses oksidasi,pelarutan / leaching, pengayaan supergen / supergen enrichment, endapan supergen hidrotermal. This allowed surface ground water to attack the granite in these areas. More recently in the ice age, mechanical erosion has removed the material, leaving the core stones or tors surrounded by clitter. Colors caused by supergene enrichment in the oxidized zone of the deposit. Supergene Enrichment *veins undergo a secondary enrichment - become more concentrated in ores. 4. Proses sedimentasi Yaitu proses pengendapan sedimen mekanis / klastik, pengendapan sedimen kimiawi, pengendapan sedimen koloid, proses diagenesa. In coastal waterways, sedimentation rates refer to the amount of material (organic and mineral) deposited by the action of water over a given interval of time. Sedimentation is measured in terms of vertical accumulation over time or sediment density per unit area over time. 5. Proses metamorfisme regional, termal, dan dinamik Metamorphic rocks are the result of the application of heat, pressure and directed stress, or some combination of these effects applied to pre-existing rock of any type. The process by which metamorphic rocks are produced is called metamorphism. There are three types of metamorphism, which are characterized by the nature of the conditions that cause them. They are; Regional, Contact, and Dynamic metamorphism Contact metamorphism Contact metamorphism is confined to rocks (often referred to as country rocks) immediately surrounding an igneous intrusion. The alteration of the surrounding country rocks is caused by heat and fluids emanating from the intruding igneous body. The zone of alteration (metamorphic aureole) can vary from only a few centimetres to several kilometres in width. The size of the alteration zone depends on the size and temperature of the intrusion. Contact metamorphism is greater round very large, hot intrusions. 6. Kombinasi dari proses-proses diatas Ref : Bahan Kuliah  T.Geo'07 Unsoed