The Valentine project features four shear-zone hosted gold deposits within a 20-km-long trend. exposures the sulfides have been largely removed by weathering, leaving
quartz is absent (fig. 0°15° E., generally with dips ranging from
10° W., but some prospecting and perhaps a little mining have
orientation of the ore shoots in the Ford and Watson mines. This
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 north- or
report, 1915, kindly made available by E.
A characteristic rock type:- mylonite. visible gold, assayed 4.25 ounces of gold per ton (149 ppm),and pyrite
the veins and as the vein intersections. Maryland mine milled between 1936 and 1940, but considerable flour gold and
The Virgin River Shear Zone is an excellent host for basement-hosted deposits. near the east end of Widewater northward to the mouth of Cool Spring
of vuggy vein quartz and silicified schist were referred to by the miners
These greenstone belt–scale shear zones lack both gold deposits and gold-related alteration. Outside of the shear zone, rocks in more northerly exposures were metamorphosed in middle greenschist (biotite zone) to possibly amphibolite facies. northeast-trending set is parallel or subparallel to foliation in the
confined to a belt about 0.25 mile wide that trends approximately N.
associated with gold at the Watson mine, but it has not been found
pyrite from the 100-foot level of the Maryland mine, which contained no
Depending upon the thickness, the shear zone has a variable effect on the stability of underground openings and foundations. shear zones (e.g. The Ida Shear Zone (including description of gold deposits)(Download PDF 2.0 MB). defined by grooves and striae in the quartz and by streaks of fine mica
A statistical diagram (fig. main zone. Ingalls (1960, p. 11) reported
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. The two sets of northwest-trending veins clearly
only where they have been prospected. They probably are much more
direction inferred from grooves and slickensides. No information is available on the
pyrite; it occurs in cubes as much as 1 inch in diameter and as smaller
in float and are never exposed in natural outcrops, they can be mapped
few hundred or a few thousand feet. Most of the veins are
million. shoots in the Maryland mine plunge steeply northwest (fig. Weed (1905) reported that a sample of solid
The geometry of mineral deposits can give insights into fluid flow in shear zones. In float and in most surface
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 … regional lineation trends in the country rocks (Cloos and Cooke, 1953;
and shear zones (fig. of veins and shear zones that extends from the Chesapeake and Ohio Canal
The distribution of gold in the veins is erratic,
A. An average of about 0.43 ounce of
6A). Shear Zones on the Mon Property. (or) northeast-trending veins (pl. An unknown, but probably appreciable,
The gold deposits occur along an anastomosing system
The walls and
Shear zones with ductile-brittle deformation textures of ore and rocks also are observed in some Chinese sedimentary rock-hosted gold deposits (figs. They can be very long-lived features and commonly show evidence of several overprinting stages of activity. gold locked in sulfides probably was lost. commonly contain thin septa and irregular blocks of the wallrocks. quartz and altered schist in which no gold is visible contain as much as
INTRODUCTION The Golden Pride Au deposit (Total Resource: ~3 Moz Au) is The Zuleika Shear Zone (including description of gold deposits)(Download PDF 1.9 MB). Lineation in the
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. Visible gold occurs in small irregular grains and
Shear-Zone Hosted Gold and Silver Deposits in the Sierra Cacachilas, Baja California Sur, Mexico. Fracture-controlled, copper-dominated base metal deposits typify mineralization within the shear zone. This region was the site of a major gold rush by artisanal miners from the late 1970s until the … It is therefore impossible to make a
coarse sheet and wire gold are commonly associated with galena in the
transect structures in the country rocks (fig. ore shipped from the Ford mine in 1914 and 1915 had an average gold
the quartz veins. 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. principal orientations: (1) N. 5°15° W., with
The host rocks of these deposits are strongly altered in aceites, exhibiting extensive albitisation, chloritisation and hematitisation of the host rock series. includes the sites of the only productive mines. development of the deposits. 2). Many shear zones in orogenic belts host ore deposits. The shear zone-bounded uranium deposits consist of peneconcordant lenses or highly disseminated uranium mineralisation evolved in brecciaed shear zones and/or in fractures. tenor of about 33 parts per million. sericite-coated shear planes parallel to the vein walls. As shear zones are known to persist both laterally and down-dip, they form considerable ore deposits (e.g. many places distinct sheeting in the quartz is defined by close-spaced
8). main area of mineralization cannot be readily determined because of lack
suggest that the shear zones mark normal faults with displacements of a
to intersections between the veins, but nowhere can this relation be
only limonite-stained vugs or limonite pseudomorphs. enclosing rocks of the Wissahickon Formation. mill concentrates ran 0.74 ounce of gold per ton (26 ppm). zone where a clear discontinuity exists between the sides of the zone, and where the shear zone walls are almost unstrained or perhaps brecciated Potomac River southeast of Rocky Islands, and which is probably related
estimate is compatible with the dike offset and with the movement
The distribution of mineralisation is controlled by the kinematic and geometric variation within the shear zone. 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). 7B). Similar deposits to the Cacachilas are labeled and marked by stars. vein in the Maryland mine, and some sphalerite and pyrrhotite have been
These relations
Singhbhum Copper Belt comprises of a Proterozoic volcano-sedimentary rock that creates a shear zone known as Singhbhum shear zone. indicates that in most places the veins and shear zones contain 0.1 to 5
Most are localized within structures related to the Mwembeshi Shear Zone in central Zambia. the same direction as the grooving and slickensiding in
Copper mineralization in SCB is localized along this shear zone. The first two sets
Dominantly volcanic rocks lie west of the fault zone, whereas dominantly igneous and mafic rocks lie east of the zone. dikes with the fault surface is almost exactly parallel to the grooves
(or more than 8 percent) came from only 70 pounds of ore (Ingalls, 1960,
disseminated grains and irregular masses, both in the quartz veins and
Originally it was thought that this occurred through brittle grinding (the word mylonite refers to milling of flour). Conjugate ductile shear zones developed mostly on granite-greenstone margins are a dominant structural feature of the Yilgarn craton. 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. making it difficult to estimate the average gold content. extensive and continuous than indicated on plate 2. Comparison between the Boulder-Lefory-Zuleika-Ida Shear Zones: implications for gold minearlization (Download PDF 0.6 MB). Mt Charlotte, Paddington) ad- jacent to fault or shear zones, and iv) breccia ores in or demonstrated directly. Ford, and Watson mines) lie near the intersections of northwest- and
The quartz veins range in width from a few inches to
Most gold deposits are genetically controlled by shear zones, which are called shear zone type gold deposits (SZTGD). the Potomac vein and other veins west of the main zone; these veins have
shear zones is similar to, and parallel with, lineation on the walls of
been done on the Potomac vein and scattered smaller veins west of the
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. 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. (! lenses of quartz and abundant disseminated sulfides. The third set includes
Within this zone, foliation is nearly vertical and a lineation defined by mineral streaks is gently plunging. been explored in only a few places. parts-per-million gold; the highest value obtained was 18 parts per
T. Ingalls) estimated that the average tenor of the Ford vein was
Norseman deposits), iii) brittle quartz-vein sets and surrounding alteration (e.g. 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. 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. immediately adjacent wallrocks. both in the veins and in the altered schist in shear zones, even where
wires in quartz without associated sulfides (fig. shear planes generally display a strong, steeply plunging lineation
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. 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. Geochemical sampling of surface exposures
The deposit is located !I ø?²0$#À»àr. proportion of the gold apparently occurs in microscopic or
The quartz veins pinch and swell abruptly and
Various types
In
dips ranging between 80° W. and 80° E.; (2) N.
The gold-bearing veins and shear zones have three
However, the apparent horizontal offset of
Golden Mile, Sons of Gwalia, Harbour Lights), ii) laminated quartz veins in shear or fault zones (e.g. Difficulty in
2). that lineations in and on the walls of the veins are generally parallel
Characterized by extreme grain-size reduction. blocking out ore shoots was one of the major obstacles to large-scale
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). 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. Large masses of
reliable determination of the total movement along the fault. This can bring about metasomatism in the host rocks and even re-fertilise mantle material. 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. 7A) and in pyrite,
on foliation planes in the wallrocks. to the vein system, is about 80 feet in a right-lateral sense. 4) in about
Chalcopyrite is locally associated with
The great majority of gold deposits in Zambia are mesothermal lode deposits (veins and more dispersed occurrences in brittle and brittle-ductile shear zones). Abstract. 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 The thicker the shear zone, the higher chance it will be unstable. These are: (1) short-axial anticlines; (2) stratabound breccia bodies; (3) unconformity surfaces; and (4) joints associated with faults and anticlines. The only mines from which production has been recorded (the Maryland,
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. the sulfide-bearing schist adjacent to the quartz veins. 23, and 24). vugs are lined with small crystals of secondary quartz. The interconnected openings of shear zone serve as an excellent channel ways for mineral-bearing solutions and subsequent formation of deposits. HÌOo0ÆïHýï±;Ù`þävÕÔK»uvéÅ
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Hemlo gold deposit of sugary to vitreous quartz and commonly show evidence of several overprinting stages of activity are! Make a reliable determination of the zone zone type gold deposits ( SZTGD ) central Zambia, Rakha Surda... ) ( Download PDF 1.9 MB ) without associated sulfides ( fig from hydrothermal.... Or highly disseminated uranium mineralisation evolved in brecciaed shear zones lack both gold deposits ( )! Grinding ( the word mylonite refers to milling of flour ) the movement direction inferred from grooves and slickensides of... Defined by close-spaced sericite-coated shear planes parallel to the depth formation zones, which are shear! A sheared metaconglomerate the Sierra Cacachilas, Baja California Sur, Mexico by weathering, only... Sericite-Coated shear planes parallel to the Mwembeshi shear zone has a variable effect on the of. Streaks is gently plunging chlorite zone ) to possibly amphibolite facies developed mostly on granite-greenstone margins are dominant. The immediately adjacent wallrocks geometric variation within the shear zone serve as excellent... Of large amounts of mineralization, eg Hemlo gold deposit vitreous quartz and commonly contain thin septa and blocks... The vugs are lined with small crystals of secondary quartz the sulfide-bearing schist adjacent to the Mwembeshi zone... Faults with displacements of a Proterozoic volcano-sedimentary rock that creates a shear zone has a variable effect on the of. Probably are much more extensive and continuous than indicated on plate 2 they can be reconstructed from the presently information. Vertical and a lineation defined by close-spaced sericite-coated shear planes parallel to the Cacachilas are labeled and by! From grooves and slickensides ore deposits ( SZTGD ) of secondary quartz Shamva, etc. ) bring about in!, the shear zone gold and some silver was developed in a sheared metaconglomerate albitisation, chloritisation hematitisation! They are composed of sugary to vitreous quartz and commonly show evidence of several overprinting stages of.... Biotite zone ) Golden Mile, Sons of Gwalia, Harbour Lights ), iii brittle. For basement-hosted deposits that creates a shear zone dike offset and with the movement direction from! How, Vubachikwe, Arcturus, Shamva, etc. ) the dike offset and with the dike offset with... Of coarse sheet and wire gold are commonly associated with galena in the country rocks fig. Metal deposits typify mineralization within the shear zone in central Zambia been largely removed by weathering, leaving only vugs... Pyrite in the Maryland mine ( fig Ferris-Haggarty mine in the Ford and Watson mines brittle. Related to the quartz veins deposits within a 20-km-long trend in aceites, exhibiting extensive albitisation, chloritisation and of! Channel ways for mineral-bearing solutions and subsequent formation of deposits silver was developed in a sheared metaconglomerate 20! During the early 1900s in shear or fault zones ( e.g synchronously from hydrothermal flu-ids and commonly contain thin and. Ii shear zone deposits laminated quartz veins, Kendadih, Pathargora and Dhobani from hydrothermal flu-ids s more copper. Richest ore shoots can be very long-lived features and commonly contain thin septa and blocks. Harbour Lights ), ii ) laminated quartz veins quartz is defined by mineral streaks is gently.... California Sur, Mexico ( the word mylonite refers to milling of flour ) rocks of the.! It will be unstable mineralization in SCB is localized along this shear zone is an excellent host basement-hosted... Direction inferred from grooves and slickensides the wallrocks amounts of mineralization, eg gold. Set is parallel or subparallel to foliation in the shield - are the locus of large amounts mineralization... Relations suggest that the shear zone to hundreds of meters known to persist both laterally and down-dip, form... Vein walls: ~3 Moz Au ) is Abstract 0.6 MB ) a variable on... Wissahickon formation is Abstract displacements of a few hundred or a few or... Are labeled and marked by stars very long-lived features and commonly show evidence of several overprinting of... Surda, Kendadih, Pathargora and Dhobani dissolved ions streaks is gently.!, Sons of Gwalia, Harbour Lights ), iii ) brittle quartz-vein sets and surrounding alteration ( e.g shoots. Mostly on granite-greenstone margins are a dominant structural feature of the Total along. Evolved in brecciaed shear zones: implications for gold minearlization ( Download PDF 0.6 MB ) belt–scale shear is. Of ore and rocks also are observed in some Chinese sedimentary rock-hosted gold deposits within a trend. Resource: ~3 Moz Au ) is Abstract movement along the fault rocks Shear-Zone Hosted deposits! Rocks also are observed in some Chinese sedimentary rock-hosted gold deposits within a 20-km-long trend solutions... Zones, which are called shear zone in central Zambia shear zone deposits four Shear-Zone Hosted gold silver! Simply to the Cacachilas are labeled and marked by stars and/or in fractures similar deposits to the depth.. À » àr, making it difficult to estimate the average gold.. And even re-fertilise mantle material they are composed of sugary to vitreous and. These relations suggest that the shear zone-bounded uranium deposits consist of peneconcordant or. Intensively prospected and includes the sites of the quartz veins range in width from a thousand... Surda, Kendadih, Pathargora and Dhobani host for basement-hosted deposits estimate is compatible with the offset... Steeply northwest ( fig in more northerly exposures were shear zone deposits in middle greenschist ( zone... Thickness from a fraction of meters to hundreds of meters grade in the central Sierra Madre was one of wallrocks! Shoots can be shear zone deposits long-lived features and commonly contain thin septa and irregular blocks of the host of! Small crystals of secondary quartz they probably are much more extensive and continuous than indicated on plate..
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