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Выпуск 83
Издание:Economic geology, 1988 г., 9 стр.
Characteristics of gold deposits on Nortern Sonora, Mexico: a preliminary report

The geology of northwestern Mexico is complex and is similar in many respects to that of southeastern California and southern Arizona. The region (Fig. 1), typical of the southern basin-and-range physiographic province of which it is a part, is characterized by elongate, northwest-trending ranges separated by wide alluvial valleys. Basement rocks in the area include Precambrian gneisses, metamorphosed andes-ites, and granites. These rocks are overlain by younger Proterozoic quartzites and limestones, Paleozoic and Mesozoic carbonate rocks, and Mesozoic volcanic, clastic, and carbonate sedimentary rocks. Mesozoic plutonic rocks and Tertiary extrusive and intrusive rocks related to volcanic activity of the Sierra Madre Occidental are widely distributed. Broad areas are underlain by plutonic and associated volcanic rocks of the Sonora-Sinaloabatholith of Cretaceous to early Tertiary (Laramide) age. The outcrop areas of the plutonic rocks are smaller in northwestern Sonora, west of Magdalena de Kino where many of the gold deposits are concentrated, than they are farther to the east and south (Fig. 2).

Выпуск 90
Автор(ы):Parry W.T., Paula N.Wilson
Издание:Economic geology, 1995 г., 20 стр.
Characterization and dating of argillic alteration in the Mercur gold district, Utah

The Mercur gold district of north-central Utah includes several sediment-hosted disseminated gold deposits which are located in the lower member of the Mississippian Great Blue Limestone. Argillic alteration of host limestone consists of illite (R3 illite-smectite <10% S) + kaolinite + quartz ± Fe oxides or pyrite. Argillized limestone has identical clay mineralogy in both oxidized and unoxidized rock. Unlike some other sediment-hosted disseminated gold deposits, variations in the Kubler index and illite/kaolinite ratios show no spatial relationship to faults or to gold distribution within the mineralized areas.

Выпуск 92
Автор(ы):David A.Mako
Издание:Economic geology, 1997 г., 2 стр.
Characterization and dating of argillic alteration in the Mercur gold district, Utah - a discussion

Wilson and Parry (1995) present data pertaining to clay alteration and K-Ar age dates for samples from the Mercur gold district. Their data record a wide spread of K-Ar ages for illite ranging from 98.4 to 226 Ma. They estimate the age of gold mineralization to be between 140 and 160 Ma and explain the wide range of ages as functions of partial thermal resetting of the clay minerals and the distance from the hydrothermal conduits. Morris and Tooker (1996) in their discussion of this paper, point out that a Mesozoic age for gold mineralization at Mercur is incompatible with several lines of long-standing regional geologic evidence that suggest a Tertiary age. In their reply, Wilson and Parry (1996) defend their position for a Mesozoic age of mineralization in part by relying on new 40Ar/39Ar age data and the fact that none of the 22 age dates is Tertiary. Although the research by Wilson and Parry may represent a good study of samples in the laboratory, there are several tenuous assumptions and contradictions of the geologic observations at Mercur that must be addressed.

Автор(ы):Parry W.T., Paula N.Wilson
Издание:Economic geology, 1996 г., 3 стр.
Characterization and dating of argillic alteration in the Mercur gold district, Utah—a reply

We would like to extend our appreciation to Morris and Tooker for their comments, discussion, and additional information that they provide pertaining to the geologic environment of the Mercur gold district, Utah. Their review of the characteristics of the Sevier orogenic belt are particularly relevant; however, such characteristics must be interpreted within the context of the additional geologic events of the region, which include the Jurassic compressional event that has been described from northern Utah and western Nevada. For this purpose, we offer the following reply.

Morris and Tooker have two main points of disagreement with our paper. First, they find the range of K-Ar ages we reported as disturbing and indicate that they date neither tectonic, hydrothermal, nor gold mineralization events; and second, they contend that all mineralized structures at Mercur must be younger than Late Cretaceous in age.

Издание:PGS Publishing, Linden Park, 2002 г., 20 стр.
Chilean Strata-bound Cu- (Ag) Deposits: An Overview

Strata-bound Cu- (Ag) deposits, long known as 'Chilean manto-type', occur along the Coastal Cordillera of northern Chile (22°-30°S) hosted by Jurassic and Lower Cretaceous volcanic and volcano-sedimentary rocks. These deposits are typical of the first stage of Andean evolution characterised by an extensional setting of the arc magmatism along the active margin of South America. Strata-bound Cu- (Ag) deposits were formed during two metallogenic epochs in the Late Jurassic and uppermost Early Cretaceous. The mineralisation took place at the time of structurally controlled emplacement of batholiths within the Mesozoic volcanic and sedimentary strata. The volcanic-hosted strata-bound Cu- (Ag) deposits invariably occur distal, but peripheral to coeval batholiths emplaced within tilted Mesozoic strata. The prevalent view that these deposits have an inherent genetic relationship with hydrothermal fluid derivation from subvolcanic stocks and dykes is contended here, because these minor intrusions are largely barren and this hypothesis does not fit well with Sr, Os and Pb isotopic data that call for crustal contribution of these elements. The strata-bound Cu- (Ag) mineralisation appears to be produced by fluids of mixed origin that were mobilised within penneable levels and structural weakness zones of the Mesozoic arc-related volcano-sedimentary sequence during the emplacement of shallow granodioritic batholiths under transtensional regimes. These hydrothermal fluids deposited copper and subordinate silver when reacted with organic matter, pyrite and/or cooled away from their heat sources. Although strata-bound Cu- (Ag) mineralisation took place during the same Cretaceous metallogenic event that formed the magnetite-apatite bodies, and Fe-oxide-Cu-Au deposits along the present Coastal Cordillera, the conceivable relationships with these other types of deposits are hampered by the inconclusive debate about the origin of the Chilean Fe-oxide deposits. However, the available data strongly suggest that the Fe oxide-rich deposits are metasomatic in origin and genetically related to contact zones of Lower Cretaceous dioritic batholiths, whereas the iron-poor volcanic-hosted Cu-(Ag) stratabound deposits constitute distal mineralisation peripheral to Upper Jurassic of Lower Cretaceous granodioritic batholiths.

Издание:PGS Publishing, Linden Park, 2005 г., 24 стр.
Chuquicamata, Core of a Planetary Scale Cu-Mo Anomaly

The copper and molybdenum mineralisation of the Chuquicamata deposit has been known since the 19' century. The deposit is located within the Codelco Norte District in the Andes Ranges of northern Chile, 200 km northeast of the city of Antofagasta. Small miners initially worked the exposed oxidised outcrops and high grade oxide veins that were the surface expression of the deposit, although industrial scale mining did not commence until 1915 with open pit exploitation of the main disseminated oxides. Mining has continued to the present day, currently removing approximately 170 000 tonnes of ore and 400 000 tonnes of waste per day.

Выпуск 91
Издание:Economic geology, 1996 г., 11 стр.
Clay alteration and gold deposition in the genesis and Blue Star Deposits, Eureka County, Nevada

The Genesis and Blue Star sedimentary rock-hosted gold deposits occur within the 40-mile-long Carlin trend and are located in Eureka County, Nevada. The deposits are hosted within the Devonian calcareous Popovich Formation, the siliciclastic Rodeo Creek unit and the siliciclastic Vinini Formation. The host rocks have undergone contact metamorphism, decalcification, silicification, argillization, and supergene oxidation.

Издание:The Geological Society, London, 2009 г., 373 стр.
Collision and collapse at the Africa–Arabia–Eurasia subduction zone (Коллизия и коллапс в Африкано-Аравийско-Евразийской зоне субдукции)

Настоящий сборник включает в себя 13 работ, в которых рассматриваются различные вопросы геодинамики, стратиграфии, истории геологического развития, магматизма, метаморфизма, кинематики региона, находящегося на стыке Африки, Саудовской Аравии и восточной Европы с позиций тектоники плит, т.е. как зоны субдукции и связанной с ней орогении.

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Выпуск 83
Издание:Economic geology, 1988 г., 23 стр.
Comparative elemental and oxygen isotope geochemistry of jasperoid in the Northern Great Basin: evidence for distinctive fluid evolution in gold-producing hydrothermal systems

This comparative geochemical study of jasperoid in the northern Great Basin is based on 65 samples from 10 Carlin-type gold deposits and 22 similar but apparently barren hydro-thermal systems. Multielement geochemistry coupled with oxygen isotope data indicate that hydrothermal fluids in barren and mineralized systems evolved in different ways, and that there are fundamental geochemical differences among the various gold-producing deposits of the area.

Much of the variation in the jasperoid geochemical data can be explained in terms of seven abstract end-member components obtained through factor analysis. Three of these components (factors) dominate the results and are related to common products of alteration and mineralization in epithermal systems of the northern Great Basin. Element associations for these factors are: factor 1: Ti02, Al203, La, K20, Sr, Fe203, Th; factor 2: Au, Ag, Sb, Si02> As, Pb; and factor 3: W, B, V, Zn, Co, Au, CaO, Ni, Mn, Cu.

Выпуск 84
Издание:Economic geology, 1989 г., 3 стр.
Comparative elemental and oxygen isotope geochemistry of jasperoid in the northern great basin: evidence for distinctive fluide evolution in gold-producting hydrothermal system - a discussion

Discriminating productive jasperoids associated with economic gold mineralization from barren jasperoids, those with no known gold association, has long been an objective of Great Basin explorationists. Holland et al. (1988) use factor analysis of a multielement geochemical data set to compare jasperoids associated with Carlin-type gold mineralization with jasperoids in barren systems. They go on to propose a genetic model for Carlin-type deposits based on their interpretation of the factor analysis results. There are problems with their approach, several of which the authors acknowledge. The geologic control for their samples is inadequate, the analytical technique used is inaccurate for several critical elements, and their statistical analysis of the data could be much simpler, easier to interpret, and useful.