Characteristics of Epithermal Deposits

Mineralization is close to the surface, to a maximum deepness of close to 2 km. The straight down range of ore is about 350 meters. Veins are for the most part frequent ore host, with breccia zones; stock work and fine grained bedding replacement also occurring. Fracture systems are frequently, but not inevitably, related to large scale volcanic collapse structures. Close connection with subaerial pyroclastic rocks and sub-volcanic intrusions. Hot springs and fumarole deposits possibly will be nearby in deposits that are not profoundly eroded. Ore and related minerals are deposited for the most part in open space filling with banded, crustiform, drusy, colloform and cockscomb textures. Gold and silver are the major economic minerals with lesser Hg, As and Sb. Gangue minerals are primarily quartz and calcite with a minor amount of fluorite, barite and pyrite.

Hydrothermal alteration is pronounced, with argillic and phyllic alteration inside a bigger propylitic envelope.

Genesis
Epithermal deposits form from dilute waters that go through a process of boiling or effervescent degassing, mixing of fluids and oxidation at temperatures that are close to 200 to 300°C. Boiling and mixing of fluids seams to be the most key cooling system.

Lithology and Mineralogy
Getting hold of practical, rock-based information from wells that are not cored is progressively more essential to drilling programs all around the world now. Investigation of core has customarily made available benchmark determinations for lithology, mineralogy, sedimentary facies, and reservoir quality and the outcome of core analysis are then utilized to standardize petrophysical logs, and as key contribution to digital reservoir models.

In wells that are not cored, log data turns into the main source of information, increased by unsophisticated and in many cases individual lithology determinations that have been obtained from cuttings. In addition, drilling progress such as fixed cutter bits modify or eradicate the textures of the rocks in the cuttings, creating visual lithological identifications even trickier. Without a doubt, modernizations are necessary to scrape together as much objective geological information as is possible from cuttings. One hopeful method is the modeling of lithology and mineralogy from whole rock elemental analysis, which are not sensitive to devastation of the rock texture. As a first try out of this advance, elemental and mineralogical data has been collected and obtained on a number of sets of core samples from carbonate evaporite reservoirs. Improved XRD sample groundwork and peak modeling means allowed more accurate quantification of Mg calcites, which is associated to MgO capacities from elemental investigations. This resulted in improved forming of calcite and dolomite fillings from essential information. Anhydrite can be easily modeled from SO3, silt and clay content can be modeled from SiO2, Al2O3, TiO2, and K2O, and small stages such as Fe2O3, MnO, P2O5, Cl, Sr, and Y make available added limitations on mineralogy. Enhanced mineralogical purposes are perceptibly important for the density of matrix and porosity calculations from petrophysical logs, as well as for evaluation of gamma ray response. Besides that, given that field wide chemostratigraphic units in carbonates differ in their origin, mineralogical limitations can assist in understanding the area.