The global historical production is estimated to be approximately 180,000 tons and about onethird of that gold comes from orogenic gold deposits frimmel 2008. New theory suggests gold deposits were formed as a result of. Gold is actually a relatively scarce element on the crust of the earth, but it occurs in trace quantities spread throughout many different kinds of rocks and in many different geological environments. Prospectivity analysis of orogenic gold deposits in saqezsardasht goldfield, zagros orogen, iran by a. Mar 18, 20 a new theory based on a simple but viable geologic model claims that over 80 percent of all commercial gold deposits were formed in a flash. We invite contributions on all aspects of geochemistry applied to these intriguing deposits. In most deposits the movement of the gold is downward, although some exhibit chemical enrichments that indicate a degree of lateral movement of the auriferous solutions. Models and exploration methods for major gold deposit types. The idea that gold concentrations are derived from host rock as the source of gold in deposits in central victoria, is not new. Box 28503, addis ababa, ethiopia 2department of geological sciences, university of vienna, althanstrasse 14, a1090 vienna, austria received december 31, 2003.
Gold occurs in a wide range of deposit types and settings, but this paper is concerned with deposits in which gold forms the main economic commodity or a coproduct. Orogeny, or mountain formation, is the result of intense upward displacement of the earths crust. Introduction to geology and resources of gold, and geochemistry of gold the case for gold an introduction to geology and resources of gold in the united states by daniel r. Mesothermal veins are known for their large size and continuation to depth, and therefore, are a major source of the world. Here is a look at the components that make up orogenic deposits. Introduction to geology and resources of gold, and. Gold deposits can still be seen today forming in some active geothermal areas. Mesothermal and greenstone gold deposits aka orogenic geology.
A proposed classification in the context of their crustal distribution and relationship to other gold deposit types. Gold deposits of zortmanlandusky, little rocky mountains, montana. As the price of gold increased dramatically in the late 1970s, so did interest in the understanding of these gold deposits. Orogenic gold deposits are the main source of gold for humanity. Hastings, 1988 this paper discusses the history and development of the gold deposits of the zortmanlandusky mine. There are six worldclass settings for magmatichydrothermal gold deposits. Detailed material for this globally important deposit type will be provided on tectonic and structural controls. Deposits can range from single small quartz veins to large and commonly highgrade, faultshear controlled systems containing in excess of 25 million ounces of gold. The massive deposits of the witwatersrand mines in south africa have produced more than 40 percent of the worlds total production of gold.
The origin of these ancient oresseveral billion years oldis controversial. Pdf parameters for the formation of orogenic gold deposits. He explains how orogenic gold formed during plate tectonic collisions and especially during continental growth. Shawe geochemistry of gold in hydrothermal deposits by samuel b. Orogenic gold deposits are gold lodes within and associated with metamorphic belts 1,7,8,9. Input data for the present study are existing gold deposits, mapped and interpreted faults, and multiscale. Definition of gold rich volcanogenic massive sulphide deposits simplified definition a lens of iron, copper, zinc and leadsulphides, with significant amounts of silver and gold, formed on or below the sea floor by hot springs on and around submarine volcanoes. Mesothermal veins are known for their large size and continuation to depth, and. The details will be debated until the sun cools, but the broadbrush classification of mineral deposits is generally understood. Pacton gold is a canadian exploration company with key strategic partners focused on the exploration and development of high grade conglomerate and orogenic gold properties located in the districtscale pilbara gold rush in western australia and the red lake district, ontario. Geologic information is provided about the regional setting, structural geology, sedimentary rocks, igneous rocks, and ore deposits of the area. I had long ago come to the conclusion, that most, if not all, the gold in the. Although the exercise and outdoor activity experienced in prospecting are rewarding, there are few thrills comparable to finding gold. Some geologists think these deposits were formed when streams deposited the gold into an.
Since the first production in 1878, almost 28 million troy ounces of gold have been extracted, worth 987 million dollars at present price causing the mine to be the most valuable in the united states. Classification of mineral deposits geology for investors. If a gold bearing area is on privatelyowned land, be sure to obtain permission from the owner in writing prior to prospecting. The development of thought and the history of investigations on ores in metamorphic terranes aretraced. The deposits occur mainly along major fault zones, in association with preserved slivers of alluvialfluvial, timiskamingtype, sedimentary rocks. Sixteen common types of bedrock gold deposits are distinguished from one another and their main geological attributes are. Violations may accrue major fines and in more serious cases, possible jail time.
Mesothermal gold deposits form half way up through the rise of the melt from the deep crust to the surface usually at a depth of less than 10 km but greater than 1 km. Geochemistry, alteration, and genesis of gold mineralization. Predictive targeting in australian orogenicgold systems. Dr richard goldfarb is a world expert on orogenic gold deposits. Nov 27, 2012 further west in victoria there is very little gold in granite eg a bit around mafeking in the grampians, and north of lancefield, and only mafeking had any significant production from deposits in granites different in the northeast of the state, eg glen wills was important. Anyone who pans for gold hopes to be rewarded by the glitter of colors in the fine material collected in the bottom of the pan. These deposits form in response to major orogenic events caused by accretion or changes in subduction direction or dip. New theory suggests gold deposits were formed as a result. Instead, the unique temporal and spatial association of this deposit type with orogeny means that the vein systems are best termed orogenic gold deposits.
In the oxidized zones of gold deposits both mechanisms have generally operated, and there are rarely sufficient criteria to distinguish which mechanism is dominant. Orogenic gold deposits, or gold deposits in metamorphic rocks, are the spatially and temporally most widespread gold deposit type, defining important exploration targets in precambrian shields and in phanerozoic orogen ic belts. Just starting out with the hobby of amateur gold prospecting and want to know where to find gold deposits. Before you get out into the field to try your hand at gold panning or metal detecting, its worth taking a moment to learn about the different types of gold deposits. In the above orogens, isotopegeochronological estimates suggest that the ore deposits were formed late in the orogenic history or even after orogeny had demonstrably ended 3,4,10,11. Australian geologist daintree, studying the layers of gold, wrote into 1866. In contrast to typical orogenic gold deposits displaying textures indicating brittleductile deformation and recrystallization, those of grass valley only display minor brittle fracturing of quartz and pyrite. Introduction ore deposits are crustal concentrations of useful elements that can be exploited at a pro. Optical microscopy and optical cathodoluminescence imaging. Syeniteassociated disseminated gold deposits in the abitibi. Gold can be described according to its natural size and nature of occurrence.
Distribution of orogenic gold deposits in relation to fault. Most ores are postorogenic with respect to tectonism of their immediate host rocks, but are simultaneously synorogenic with respect to ongoing deepcrustal. Examples of such deposits are numerous and include the tomingleycaloma sytem in nsw, the gympie deposit in queensland, and the slatebelt deposits of victoria e. Prospectivity analysis of orogenic gold deposits in saqez. Nov 10, 20 dr richard goldfarb is a world expert on orogenic gold deposits.
Geology of gold deposits perspective in 1988 monograph. The deposits consist of disseminated sulfide replacement zones with variably developed stockworks of quartz. On the source of orogenic gold geology geoscienceworld. A rational geological classification of the commonly recognized lode gold deposits is feasible if it is based on the geological settings of the deposits, host rocks, nature of mineralization and geoche mical signature.
Gold deposits in the pine creek inlier likely formed moreorless simultaneously with emplacement of the posttectonic cullen batholith at 18351820 ma. Geochemistry, alteration, and genesis of gold mineralization in the okote area, southern ethiopia debele j. The effort to understand the geology of gold was perhaps mans first serious effort at understanding the earths rocks and minerals. Gold occurs mainly as native metal, alloyed with silver andor other metals, and as tellurides.
These deposits formed from the archaean to phanerozoic at crustal depths of more than 4 km. Scientific definition gold rich volcanogenic massive sulphide deposits. Oxidation and secondary enrichment of gold deposits. Gold prospecting how to find gold in the united states. Timing of gold and arsenic sulfide mineral deposition at the. A naturally occurring alloy of gold and silver is known as electrum. The term mesothermal veins is really a sack term, referring simply to the depth formation. The approach to modelling these systems is based on the following assumptions about orogenicgold systems at the deposit to camp scale. Mcqueen crc leme, australian national university, canberra, act 0200 and school of rehs, university of canberra, act 2601.
Orogenic deposits are the source of much of the worlds gold. Orogenic gold deposits bohlke, 1982 dominantly form in metamorphic rocks in the mid to shallow crust 515 km depth, at or above the brittleductile transition, in compressional settings that facilitate transfer of hot goldbearing fluids from deeper levels goldfarb et al. Jul 29, 20 geologists, are known to have more opinions than economists, so it should come as no surprise that the classification of mineral deposits, is an ongoing hot topic. The key parameters accounting for their formation remain under discussion. Gold is commonly associated with the sulfides of antimony, arsenic, copper, iron, and silver. The terms metamorphosed, metamorphic, and metamorphogenic as applied to ores are also considered. A distinct group of gold deposits in the abitibi greenstone belt is spatially associated with quartzmonzonite to syenite stocks and dikes.
The objectives of this paper are to provide an update on gold deposit models, and what new approaches and techniques can now be used to find gold deposits. Orogenic gold deposits have formed over more than 3 billion years of earths history, episodically during the middle archean to younger. Orogenic definition of orogenic by the free dictionary. A new theory based on a simple but viable geologic model claims that over 80 percent of all commercial gold deposits were formed in a flash.
1206 1139 1223 479 444 1012 142 1419 956 740 600 1401 489 1568 1343 1131 309 1564 981 1248 1488 1335 1008 83 1476 1261 777 1321 896 445 1144 1393 952 1175 1463