Vein Zone Research Articles

Geophysical exploration for epithermal gold deposits: Case studies from the Hishikari Gold Mine, Kagoshima, Japan

Various geophysical techniques were applied experimentally to exploration for epithermal gold deposits. The Hishikari gold?silver deposit, located in northeastern Kagoshima, Kyushu, Japan, was selected for this study. This paper presents the results from these case studies and discusses the applicability of each method in several stages of the exploration; the reconnaissance stage, the detailed follow-up stage and the final stage where the surveys are directed at detecting veins. The results are summarized as follows; 1. A high-gravity anomaly was interpreted as the swollen basement. This subsurface structure was considered to be local doming of basement associated with volcanic activity. Local gravity highs are worthy of notice because the doming of basement might cause fractures; 2. A resistivity cross-section was characterized by three layers; an uppermost layer with high resistivity (100?1000 Wm) corresponding to unaltered volcanic rocks, an intermediate layer with low resistivity (3?8 Wm) corresponding to altered volcanic rocks and a bottom layer with relatively high resistivity (80?200 Wm) corresponding to the basement. Resistivity mapping and sounding are useful to identify lithologies and structures that may control gold mineralization; 3. IP anomalies (high chargeability) within the area of low resistivity are the most important indicators of vein zones. For this reason, in the detailed follow-up stage and the final stage of exploration, IP surveys play the most important role.

Cretaceous epithermal Au-Ag mineralization in the Muju-Yeongam district, Republic of Korea: Muju mineralized area.

The gold-silver vein deposits of the Muju area, about 180km SSE of Seoul, are examples of the epithermal gold-silver deposits of the Republic of Korea. The deposits are composed of quartz and calcite veins that crosscut Precambrian gneiss and Cretaceous volcanic rocks (dacite porphyry of ≈ 130 Ma, and rhyodacitic crystal tuff) and intrusive rocks (porphyritic granite of ≈ 102 Ma). Mineralization occurred in four stages (I, II, III, and IV) which filled preexisting fault fracture zones. Hydrothermal wall-rock alteration up to 10m wide is characterized by sericitic, silicic, chloritic and pyritic assemblages. Pipe-like vuggy silica alteration characteristically occurs at the innermost and surface zones of dacite porphyry-hosted quartz veins. K-Ar dating of alteration sericite (≈ 103 Ma) indicates a late Cretaceous age for ore mineralization, which is probably associated with the intrusion of the porphyritic granite. Fluid inclusion and stable isotope data show that electrum, argentite, sphalerite and galena were deposited at temperatures between 260° and 180°, from fluids with salinities between 3.2 and 0.5 wt. % NaCl equiv.. Fluid inclusion evidence of boiling suggests pressures of ≈ 40 bars during late portions of stage II mineralization, corresponding to depths between 150 and 400m, assuming lithostatic and hydrostatic loads. Equilibrium thermodynamic interpretation of mineral assemblages indicates that the gold-silver-depositing fluids had a pH of 4.4 to 5.4 and log activities of S2 and 02 of -12 to -16 atm and -37 to -38.7 atm, respectively. Gold-silver deposition was a combined result of the cooling of ore fluids through mixing with less-evolved meteoric waters and the decrease of sulfur activity due to sulfide precipitation. Sulfur isotope compositons of stage II sulfide minerals range from 0.5 to 5.9 per mil, yielding a δ34Σs value near 4 per mil which indicates a local igneous source for sulfur. The oxygen and hydrogen isotope values of hydrothermal fluids (δ18O=-6.6 to -1.3 per mil, δD=-83 to -73 per mil) are consistent with meteoric water dominance approaching unexchanged meteoric water values.

Application of a Selective Phase Extraction Procedure to Samples from the Adamello Contact Aureole (Italy)

AbstractHydrothermal veins, rich in Ti, Zr, rare earth elements (REE’s), and actinides, occur in the pure dolomitic marbles of the Adamello contact metamorphic aureole. A selective phase extraction using 9M HC1 was applied to samples from within and near these veins to chemically separate acid-soluble phases from residual phases, and to study the associations of U, Th, and REE’s with these phases. The samples were from the phlogopite, titanian clinohumite, and forsterite vein zones, and from the country rock. The effects of the extraction were studied by SEM/EDS and by chemical analysis. Isotopes of U and Th were analysed by alpha-spectrometry.The chemical data and SEM/EDS results indicated that dolomite, calcite, apatite, and much of the pyrrhotite were dissolved by the 9M HC1, whereas spinel, phlogopite, titanite, chal copy rite, and zirconolite were among the acid-resistant phases. In all vein samples, the REE-patterns of acid-soluble phases were consistent with the dissolution of REE-rich apatite. In samples from the phlogopite zone, the majority of U, Th, and REE’s were in residual phases, and the REE pattern of the residue was similar to that of REE-rich titanite. In the titanian clinohumite zone, a substantial proportion of these elements were in acid-soluble phases, and the REE pattern of the residual phases resembled that of zirconolite. Clinohumite was partially dissolved by the HC1 treatment. The sample from the forsterite zone contained substantial amounts of REE's in acid-soluble phases, whereas Th and U were mostly in residual phases. The dolomite (country rock) samples contained small amounts of an acid-resistant, uranium-rich phase which, while only comprising about 0.2% of the mass, accounted for 40–60% of the uranium present.

Fluid inclusion studies of zoning in the Dachang tin-polymetallic ore field, People's Republic of China

The Dachang tin-polymetallic ore field, Guangxi, People9s Republic of China, is one of the largest in the world and contains the Changpo, Bali, and Longtaoshan tin-base metal deposits, the Dalfulou black shale-hosted cassiterite-sulfide deposit, and the Lamo Cu-Pb-Zn proximal skarn deposit. These are hosted by Devonian carbonate-rich sediments metamorphosed to hornblende hornfels facies near the underlying Yanshanian Longxianggei granite (91 Ma). Plutonic intrusion and relevant mineralization are controlled by the north-northwest-trending Longxianggei and Changpo anticlines. The conduit for distal skarn solutions was a reverse fault (F1). Tin mineralization at Changpo is genetically related to the S-type Longxianggei granite with proximal skarns precipitated near its contact and distal ores 300 to 500 m vertically away from the contact.Hydrothermal alteration is grossly zoned outward from the granite contact as follows: (a) proximal ore skarn zone (garnet and pyroxene), (b) tourmaline-silicified zone, (c) sericite (+ or - cassiterite) zone, and (d) carbonate(-sulfosalt) vein zone. Zones b to d do not occur above the Lamo deposit whereas zone a is missing directly below the large Changpo deposit but occurs lateral to it. Nearest to the granite outcrop, the Lamo Cu-Pb-Zn proximal skarn is developed with a temporal sequence of stages: (A) garnet-vesuvianite-wollastonite + or - diopside, (B) Ca amphibole-epidote-fiuorite-quartz, (C) biotite-sericite-sulfides, and (D) sulfides-carbonate-chlorite. Distal skarns have the following temporally and spatially distributed stages: (1) tourmaline-quartz-cassiterite, (2) arsenopyrite-cassiterite (+ or - other sulfides), and (3) sulfosalts-carbonate (most distal).There is a zonal pattern of both temperatures and ore fluid compositions deduced from fluid inclusions as follows: proximal skarn zone: 450 degrees to 600 degrees C, CO 2 /CH 4 35 wt percent NaCl equiv; tourmaline-silica zone: 350 degrees to 450 degrees C, CO 2 /CH 4 = 0.10 to 10.00, salinity = 12 to 30 wt percent NaCl equiv; sericite zone: 250 degrees to 350 degrees C, CO 2 /CH 4 >10, salinity 2 dominated, no CH 4 , salinity = 6 to 8 wt percent NaCl equiv.Daughter crystals include antarcticite (CaCl 2 . 6H 2 O), halite, sylvite, carbonate, MgCl 2 . 6H 2 O), and fluorite. Thermodynamic calculations based on fluid inclusion composition and measured temperature show that f (sub O 2 ) values of the ore-forming stages were very low, well below the FMQ buffer and increased from early to later stages. Tin precipitation was affected by a low oxygen fugacity of ore fluids partly resulting from the occurrence of black shale, and a decrease in temperature.

REE-bearing minerals in a Ti-rich vein from the Adamello contact aureole (Italy)

Zirconolite, aeschynite-(Ce), titanite and apatite have been found as minor or accessory minerals in a Ti-rich (TiO2=2.1–4.5 wt.%) hydrothermal vein occurring in dolomite marbles at the contact with a tonalite intrusion of the Tertiary Adamello batholith (northern Italy). The vein consists of four distinct mineral zones, comprising from margin to center: (1) forsterite+calcite, (2) pargasite+calcite+titanite+sulfides, (3) phlogopite +calcite+titanite+sulfides, and (4) titanian clinohumite +spinel+calcite+sulfides. Zirconolite occurs in two vein zones only: in the phlogopite zone it is invariably anhedral, often corroded, and exhibits complex chemical zonation patterns. In the titanian clinohumite zone zirconolite is idiomorphic and characterized by a pronounced discontinous chemical zoning, but shows no evidence of corrosion. The considerable compositional variation observed for zirconolite (in wt.%: ∑(REE2O3)=0.74–16.8, UO2=0.59–24.0, ThO2=0.67–17.1) is due to the zoning, and may be attributed to four major substitutions described by the exchange vectors: 1. (Th, U) (Mg, Fe2+) Ca-1 Ti-1 2. REE Al Ca-1 Ti-1 3. REE Fe2+ (Nb, Ta) Ca-1 Ti-1 4. Hf Zr-1

Metamorphogenic Au‐W veins and regional tectonics: Mineralisation throughout the uplift history of the Haast Schist, New Zealand

Abstract Gold‐scheelite (Au‐W) vein mineralisation in the Mesozoic Haast Schist (Otago, Alpine, and Marlborough Schist belts) resulted from metamorphic dewatering and fluid channelling periodically throughout the >100 Ma tectonic history of the schist belt. The earliest metal mobilisation occurred during synmetamorphic vein formation and was both accompanied and succeeded by ductile deformation. Structural style of deformation within vein zones became progressively more brittle as mineralisation accompanied Mesozoic‐Tertiary isostatic and extension‐related uplift of the Otago Schist. Rapid tectonic uplift in the Late Cenozoic resulted in mineralisation in the narrow belt of Alpine Schist along the Alpine Fault. The wide range of structural styles of vein systems seen in the Haast Schist represents different erosion levels exposed in tectonic zones. Geothermal gradients during Otago Schist mineralisation appear to have been close to normal, whereas mineralisation in the Southern Alps took place under anoma...

Sulfur isotope studies of the felbertal scheelite deposit, eastern alps

The Felbertal scheelite deposit is the largest known strata-bound tungsten concentration. It lies in an up to 400 m thick rock pile in the lowermost part of the volcanic rock sequence, probably of the Early Paleozoic Habach Formation. Both ore fields (eastern and western) have been affected by Variscan and Alpine metamorphism and tectonism, resulting in a remobilization of the ore mineralization. This ore deposit and the neighboring rocks show a strikingly low sulfur content. The eastern field with one major orebody has very little sulfide mineralization. The western field, with 8 orebodies (K1–K8) and two remobilized vein zones (S1 and S2), reveals somewhat more minor sulfide enrichments that are mainly within and around the K1 and K2 orebodies and in some parts of the interlayered schist sequence. Sulfur isotope compositions of 90 sulfide minerals (37 pyrrhotite, 20 chalcopyrite, 19 pyrite and 11 molybdenite and/or WS2-MoS2 solid solutions and 3 Pb-Bi sulfosalts, including 7 sulfides within scheelite grains) from 60 ore and host rock samples have been determined with a standard error of less than ±0.2 per mil. All data range from −3.6 to +4.3 δ34S‰. There are small differences in the sulfur isotope values from place to place and in time from the first and second to the third generation. In the western field, the K1 orebody differs from other orebodies (K2, K4, K7) due to isotopically heavier δ34S values. The three scheelite generations show differences in the δ34S values of the sulfide microphases within scheelite grains, from +1.0 to +4.3 per mil for the first and the second, and from −1.8 to −3.3 per mil for the third generation. Sulfide phases within molybdoscheelites may have crystallized under the same conditions as the other coeval sulfide minerals in the same orebody. They commonly formed later than scheelite. These changes may be explained using data from Ohmoto and Rye (1979): Small changes in temperature, pH, and/or $$f_{O_2 } $$ may result in large changes in the δ34S values with the precipitation of isotopically heavier sulfides under more reducing conditions. Only four samples with sulfide mineral pairs show isotopic equilibrium. All others display some disequilibrium. We suggest that the sulfides in the ores and surrounding volcanogenic host rocks formed contemporaneously from the same hydrothermal ore fluids, and that the sulfur species in these fluids may have been dominantly H2S.

A histochemical study about the zonal distribution of the galactose-binding protein in rat liver.

1. Dog intestinal alkaline phosphatase (IAP), an asialoglycoprotein, appeared to be a good marker for the histochemical detection of the galactose specific binding protein in cryostat sections of rat liver. 2. Binding of IAP to the receptor is optimal at neutral and slightly alkaline pH values. The binding could be inhibited by galactose and galactose containing sugars, whereas glucose and mannose did not show any effect. In contrast to fetuin itself desialylated fetuin completely inhibited IAP binding. Pretreatment of sections with phospholipase C or with trypsin inhibited IAP binding; collagenase did not show any influence. 3. The presence of the galactose-binding protein showed a distinct zonal distribution. In the area around the central vein (zone 3) the highest IAP binding capacity was found.

Relationship of Serum α-Fetoprotein to the Severity and Duration of Illness in Patients With Viral Hepatitis

Using a radioimmunoassay which detect concentrations of alpha-fetoprotein as low as 5 ng per ml, 38% of 176 patients with viral hepatitis compared with health volunteers and patients with chronic diseases not affecting the liver. When separated into two groups based on histological classification of liver biopsy specimens, differences in the degree and frequency of increased serum alpha-fetoprotein were related to the severity of the hepatic lesion. Of 75 patients with the lesion of viral subacute hepatic necrosis, in which zones of necrosis bridge adjacent portal triads or central veins, 52% had increased values, and 12% had levels ranging from 500 to 3300 ng per ml. In contrast, only 28% of the 101 patients without bridging necrosis had increased values, and none had levels that exceeded 500 ng per ml. In the patients with subacute hepatic necrosis, comparison of alpha-fetoprotein concentrations with the duration of illness indicated that the protein rose to peak levels in serum as the SGOT was declining. This was confirmed by serial observations in 10 patients. Thus, the increase of alpha-fetoprotein in the sera of patients with severe hepatitis occurs as liver necrosis is subsiding. Due to other known features of alpha-fetoprotein, it is intriguing to speculate that the increase in serum levels of this protein in viral hepatitis reflects hepatic regeneration after parenchymal damage.

Neutron activation analysis of gold in Archean igneous and metamorphic rocks of the Rice lake-Beresford lake area, southeastern Manitoba

Gold abundances determined by the method of neutron activation are reported for 26 replicate analyses of a variety of igneous and metamorphic rocks. Samples analyzed come from scattered locations in and adjacent to an Archean greenstone belt containing numerous low-grade gold-quartz veins. Most of the richer veins are enclosed by mafic intrusions. The average gold content of each of the rock types is as follows:Rock Type No. of analyses Au (ppb)Northern Granites; quartz diorite: 4 1.9 + or - 1.2Manigotagan Gneissic Belt; paragneiss: 2 0.6 + or - 0.4associated quartz monzonite: 2 0.3 + or - 0.1Rice Lake Group; metavolcanics: 3 0.3 + or - 0.2Mafic intrusives; gabbro, diabase: 2 18.2 + or - 1.5Central plutons; quartz diorite: 5 1.1 + or - 0.6related felsic porphyry dykes: 2 6.1, 1.1Altered diabase wall-rock and vein zone: 6 0.5-325Gold abundances for the quartz diorite, quartz monzonite and metavolcanic groups are fairly typical of younger rocks of similar composition. Explanations are put forward to account for the unexpectedly low gold content of the paragneiss samples and relative gold enrichment in one felsic dyke sample.There is evidence to indicate that the mafic intrusions may be the source rocks of the gold. Thus, in addition to the spatial relationship of the richer veins to the mafic intrusions the latter also contain an order of magnitude more background gold than other rocks in the area. Furthermore, gold is apparently depleted in altered diabase wall-rock adjacent to a vein in the San Antonio gold mine.Non-repeatable replicate analyses observed in some mafic samples may be due to inhomogeneous distribution of gold between powder aliquots resulting from an erratic distribution of gold-rich host minerals.

MATERIAL COMPOSITION CHANGES IN THE GREISENIZATION OF KOUNRAD MASSIF GRANITES

Greisenization does not occur apart from ore bodies associated with the Kounrad granite massif. Primary minerals in granite altered and replaced during greisenization are quartz, feldspars, biotite, sphene, ore minerals, and apatite. Zircon, cyrtolite, and monazite are virtually unaffected by greisenization. Greisen-introduced minerals are muscovite, rutile group minerals, pyrite, fluorite, topaz, and molybdenite. Greisenization of Kounrad granite massif resulted in addition of more material than leached in all levels except at the base of vein zones. The excess of addition over leaching in middle and upper levels is mainly associated with upward migration of material. The value of total and individual factors of addition and leaching depends primarily on original rock composition more so than original porosity and rock structure. --R.M. Hutchinson.

Uranium deposits of the northern part of the Boulder Batholith, Montana

Uranium minerals and radioactivity anomalies occur in many silverlead veins and chalcedony veins and vein zones in the Boulder batholith of southwestern Montana. Pitchblende has been identified in a few silverlead veins. These silver-lead veins occupy shear zones along which there is no evidence of large-scale lateral displacement. The wall rock adjacent to the veins is intensely silicified and sericitized quartz monzonite and granodiorite. The veins have yielded substantial quantities of lead, silver, zinc, and gold. The silver-lead veins consist principally of galena, sphalerite, tetrahedrite, chalcopyrite, and pyrite in a gangue of light- to dark-gray quartz, altered rock, gouge, and subordinate chalcedony and carbonate minerals. No anomalous radioactivity nor uranium minerals have been found in similar veins in prebatholithic rocks of the area.Chalcedony veins and vein zones, some of which are uraniferous, are distinctly different from the silver-lead veins and, with a single exception, are known only in the batholith. The chalcedony vein zones consist of one or more discontinuous stringers or veins of chalcedony and microcrystalline quartz in silicified and sericitized quartz monzonite and granodiorite, and in less strongly altered alaskite. Only small amounts of silver ore have been produced from these chalcedony veins and vein zones. All of the veins are early Tertiary in age, but the silver-lead veins probably are older than the chalcedony veins. Uranium is closely associated with chalcedony and microcrystalline quartz in both types of veins. This association suggests that all of the uranium in the area is of the same age. If so, some of the silver-lead veins must have been re-opened during the period of chalcedony vein formation.

The Chicote tungsten deposit, Bolivia

Chicote district, situated in the eastern part of the central Bolivian Andes 65 km. N N E of Oruro, is one of the larger tungsten producers of the country. The deposit is of the cryptobatholitic type. There are narrow, mineralized fissures in Devonian shales above an unexposed intrusive...The only tungsten mineral is wolframite associated with large quantities of pyrrhotite. The vein zone has a vertical range of 1300 meters without any pronounced change in the mineral content. The district is composed of a fringe zone of tin veins surrounding a central core of wolframite veins.

On differences in chemical composition between the central and marginal zones of granite veins, with further evidence of exchanges between such veins and the contact rocks

In a former paper attention was directed to the possibility of exchanges between granite veins and the rocks in contact with them. Some chemical analyses of such veins and their contact rocks, though not specially directed to the point in question, seemed to suggest that in some cases lime and soda had been carried inwards from the contact rocks into the granite veins, while potash, and probably the iron oxides and magnesia, had been carried outwards from the veins into the contact rocks. The analyses which accompany the present paper were undertaken with the view of testing the suggestions then raised, and the specimens now analysed have been selected from particular zones in the two series of rocks, with the view of detecting what variations of composition, if any, exist between the rocks of these various zones. It was believed that if such exchanges had actually taken place, a series of analyses, embracing on the granite side one analysis of a specimen from a central and another from a marginal position in each case, and on the side of the contact rocks one from a proximal and another from a distal position, would give results that would conclusively show whether there were such co-relative differences as could be explained by the passage of substances from the one side to the other and vice versâ. Such analyses have been made in the case of five granite veins ( A ) rising through the quartz schists to the west of the Spey, and exposed