Ore-bearing Zone Research Articles

The Birkachan Epithermal Au–Ag Deposit in the Kedonsky Middle Paleozoic Volcanic Belt (Russian Northeast)

The Birkachan deposit in the Middle Paleozoic Kedonsky Volcanic Belt (KVB) is unique in Northeast Russia for its stockwork epithermal Au–Ag ores. The deposit is located in the northeastern part of the Gurnik volcanotectonic depression, in the Kedonsky segment of the KVB. The deposit is localized in the lying side of a large sublatitudinal thrust fault, due to which it was overlain in the Jurassic–Early Cretaceous by allochthon rocks and, therefore, was slightly eroded, as evidenced by the preserved fragments of the argillisite cap. The ore-bearing Gurnik sequence is composed of felsic tuffs and lavas with intercalations of ignimbrites. The main ore-bearing zone of the Birkachan deposit is 4.5 km long and 200–300 m wide consists of several echelon-like vein zones of northeast strike, falling to the southeast at angles of 55°–70°. Most of the ore bodies are linear stockworks. Single, lenticular rich ore bodies represented by mineralized breccias have been found at deep horizons. In the section, the system of ore bodies of the Birkachan deposit forms a fan-shaped structure. The main textures of ores are vein-disseminated, breccia, and rhythmically banded. The ores are enriched in comparison with the upper continental crust in a rather narrow range of elements (Au, Ag, Sb, As, Mo, W, and Li) and are poor in rare-earth elements, among which light lanthanides predominate. The sulfide grade of ores is 0.1–0.5%. The vein minerals in ores are dominated by quartz, sericite, and siderite. Among the ore minerals, pyrite dominates, with fahlore, native gold and chalcopyrite, and minerals of the series acanthite → Se–acantite → naumannite, pearceite, and Se–pearceite being less common. The average fineness value of native gold is 643‰. The parameters of mineral-forming solutions correspond to typical medium-temperature fluids of epithermal low-sulfidized deposits: homogenization temperature of 93–291°С, salt concentration of 0.2–7.0 wt % eq. NaCl, and fluid density of 0.71–0.99 g/cm3. The main indicators of fluid composition are CO2/CH4 = 15.8–23.6, Na/K = 2.3–4.3, and K/Rb = 2007. The prospects for increasing the reserves of Au and Ag are associated with further study and exploration of the flanks and deep horizons of the deposit.

Possible lowering of the preg-robbing activity of carbonaceous shales from the Kirovsk-Kryklinsk ore-bearing zone during gold cyanidation

Possible lowering of the preg-robbing activity of carbonaceous shales from the Kirovsk-Kryklinsk ore-bearing zone during gold cyanidation

MINERALOGY AND GEOCHEMISTRY OF DIORITES AND QUARTZ DIORITES OF THE BOLSHOY KARAN GOLD-PORPHYRY DEPOSIT IN THE SOUTHERN URALS

The paper provides information on the chemical composition of intrusive diorites the gold-porphyry deposit of Bolshoy Karan, located in the northern part of the Voznesensk-Prisakmar structural zone (MUF), in the north of the Uchaly ore district.
 Additional information is given on 1) primary magmatic, 2) accessory, 3) hydrothermal-metasomatic and 4) ore minerals. Special attention is paid to the geochemical features of accessory minerals from the ore-bearing zone diorites.
 According to the Nb/Yb and Th/Yb ratios in gabbroids, taking into account other materials, geodynamic reconstructions were carried out, as a result of which groups of gabbro-diorites formed in the Voznesensk-Prisakmar zone in areas with oceanic, island-arc and subcontinental types of crust, smelted from depleted and enriched mantle sources, were identified. The Bolshekaran-Voznesensk-Karagaikul ore-bearing zone is confined to an area with a thick crust of the island-arc or subcontinental type.

Quantifying mass changes during hydrothermal alteration in listwaenite-type mercury mineralization, Tavreh area, northwestern Iran

The Tavreh mercury prospect, a listwaenite-type alteration/mineralization system, is located c . 90 km west of Khoy in northwestern Iran. Tavreh is hosted within the Khoy ophiolite zone. Three types of listwaenites have been recognized in the Khoy ophiolite: silica, silica-carbonate and carbonate. Of these three, Hg mineralization at Tavreh is spatially and genetically associated with the silica-type listwaenite, also known as berberite. Alteration and mineralization at Tavreh are restricted to a faulted contact between shale and serpentinite. The Tavreh listwaenite is inferred to form from the hydrothermal alteration of brecciated serpentinite. Major mineralogical changes resulting from this alteration include the decomposition of serpentine-group minerals and the formation of silica phases. In this study, the mass changes of 18 listwaenites from Tavreh were assessed relative to the least altered serpentinites. To illustrate these changes quantitatively a comparative analysis of three different methods of calculating mass change was undertaken using Grant's isocon analysis, MacLean's equation and Gresens’ equation. Results from the three methods are similar. Listwaenite alteration was associated with a large increase in SiO 2 (44.4, 36.2, 63.9%, respectively). MgO and loss on ignition were depleted (−34.8, −36.9, −36.6; −8.5, −9.3, −8.3%, respectively) and Al 2 O 3 was relatively unchanged (0.7, 0.6, 0.9%). Mercury is the most enriched rare element in altered rock (375.1, 346.8, 474.6 ppm). Arsenic, Pb, Au and Sb were also enriched. The intensity of mass changes of the various alteration components increases significantly from the serpentinite wall rock towards the listwaenite alteration and the ore-bearing zone. Therefore, the mass balance method can probably be used to locate mineral deposits from a few hundred metres and to explore for blind mineral deposits.

Состав минералов (апатит, магнетит, ильменит и др.) как отражение процессов формирования рудных тел и расслоенности в Кусинской габбровой интрузии (Южный Урал)

Research subject . In this research, we carried out a series of mineralogical, petrological and geochemical studies to investigate ore zones present in the Kusa ilmenite-magnetite deposit located within the boundaries of a similarly-named laminated gabbro massif. Here, ore bodies occur at various intrusion horizons among laminated apogabbroid amphibolites of a different basicity. In the intrusion section, the composition of halogens (Cl, F) in co-existing fluid-bearing minerals (apatite, am-phibole, staurolite) was analyzed. Materials and methods . In order to investigate the composition of mineral samples, their polished sections were examined using an electronic-microprobe analyzer JXA-5. The content of petrogenic and microelement components (CRF and ICP-MS methods) in the rock and ore samples was determined using the facilities of the Laboratory of Physical and Chemical methods, UBRAS Institute of Geology and Geochemisty. Results. It is established that the content of Cl and F in the apatite, amphibole and staurolite under study, as well as the chemical composition of ilmenite, magnetite, and hombombite components, depend on the position of the ore bodies in the intrusion. Thus, the apatites from the near-ore rocks in the central part of the deposit showed the highest Cl concentrations of up to 4.1%, while those located in the near-contact parts of the intrusion demonstrated a much lower Cl content of 2%. The central ore-bearing zone having the maximal Cl content features the largest formation of ore bodies, which (including magnetite) contain higher amounts of Fe 2 O 3 , Cr and V The presence of fluid-bearing minerals (apatite, scapolite, etc.) with high chlorine concentrations of up to 2.44% is this deposit is established. Conclusions. The identified peculiarities of halogen distribution in the apatite of bipyroxene gabbro, as well as the inheritance of relations TiO 2 /FeO in bipyroxene gabbro, in massive magnetite-ilmenite ores and in near-ore rocks point to a single magmatic source of these formations.

Water quality and solute sources in the Marsyangdi River system of Higher Himalayan range (West-Central Nepal)

Surface waters, cold and hot springs were collected in different catchments along the Marsyangdi basin, in the Himalayan Range of West-Central Nepal, during the post-monsoon season in 2017 and analyzed for major ions and trace elements, with the aim of assessing the sources of dissolved species and to contribute in watershed planning. The major element data indicate that surface waters coming from the Tethyan Himalayan Sequence (THS) range from the Ca-Mg-HCO3 to the Ca-Mg-HCO3-SO4 water-types and reflect a two-component mixing of waters from carbonate- and sulfate-bearing sources. The latter component is attributable to sulfide oxidation with minor silicate weathering. In the Greater Himalaya Sequence (GHS), alteration of pedogenetic carbonates formed in response to silicate weathering under a variable CO2 gas pressure dominates, yielding a Ca-HCO3 signature. The stability diagram in the K2O-Al2O3-SiO2-H2O system and the paired increases in Ca2+, Na+, K+ and silica indicate that degradation of silicate minerals through kaolinization and possibly plagioclase albitization reactions is the main process for hot groundwater. Cold and hot springs define a trend of increasing Li, SiO2 and Cl−, suggesting that lithium was leached from silica-rich sources, such as pegmatite dykes and sills occurring in host rocks, and concentrated into halite-bearing salt aquifers. In hot waters Sb, As and Tl exceed the EU and USEPA thresholds. Tl is usually incorporated into pyrite and correlates with Li indicating the occurrence of an ore-bearing zone possibly related to hydrothermal activity at the transition zone between THS and GHS, as suggested by the relatively high Ba, Ni, Cu, Sb, As and Mn contents. The obtained data on water quality have significant implications for people living along the Upper Marsyangdi River in the management of water resources, especially in terms of the enhancement of cold water aquaculture and hot water uses for recreation purposes and tourism.

Geology, geochemistry and gold-ore potential assessment within Akimov ore-bearing zone (the Altai Territory)

The article considers the geological setting of ore-bearing zone. Geochemical zoning of secondary dispersion haloes within Akimov ore-bearing zone was analyzed. Based on analytical data, distribution of gold mineralization trace-elements was examined. Geochemical associations were identified, analyzed and geometrized. The structure of abnormal geochemical field associated with gold-silver mineralization was determined. Three promising areas for exploration activities were identified.

Tectonophysics of hydrothermal ore formation: an example of the Antei Mo–U deposit, Transbaikalia

The Antei deposit of the southeastern Transbaikalian region is one of the largest uranium mines in Russia. It is hosted by the Late Paleozoic granitic basement of the Streltsovskaya caldera and was formed as a result of Late Mesozoic tectonothermal activity. Vein and stockwork–disseminated molybdenum–uranium mineralization at this deposit is controlled by zones of intense hydrothermal alteration, cataclasis, brecciation, and intense fracturing along steeply dipping faults, which acted as conduits for mineralizing fluids and hosts to the ore bodies. The upper edge of the ore-bearing zone is located at a depth of 400 m, and its lower edge was intersected at a depth of 1300 m from the day surface. The conditions of ore localization were determined using structural–geological and petrophysical studies coupled with numerical modeling of the effects of gravitational body forces at purely elastic and postcritical elastoplastic deformational stages. The dynamics of the tectonic stress field in the rock massif was reconstructed using the results of mapping of morphogenetic and kinematic characteristics of fault and fracture systems, as well as data on petrography and mineralogy of rocks and vein-filling material. It was shown that the fault framework of the deposit was formed in four tectonic stages, three of which took place in the geologic past and one of which reflects recent geologic history. Each tectonic stage was characterized by different parameters of the tectonic stress–strain field, fault kinematics, and conditions of mineral formation. The following types of metasomatic rocks are recognized within the deposit: high-temperature K-feldspar rocks and albitites (formed during the Late Paleozoic as the primary structural elements of a granitic massif) and Late Mesozoic low-temperature preore (hydromicatized rocks), synore (hematite, albite, chlorite, and quartz) and postore (kaolinite–smectite) rocks. The following petrophysical parameters were determined for all rock types: density, effective porosity, wetand dry-rock shear (S-wave), and compressional (P-wave) velocity. Ultrasonic measurements were made to obtain the dynamic Young’s modulus, shear modulus, bulk modulus, and Poisson’s ratio. The results confirm that all studied lithologies (host granites, K-feldspathized rock with albitites and hydromicatized rocks) have drastically different petrophysical parameters. These values were used as the basis for tectonophysical modeling of Late Mesozoic synore deformation induced by gravitational forces. It was shown that the domains of most intense deformation are confined to the intersections of submeridional fluid-conducting faults with sublatitudinal K-feldspathized and albitized zones, which acted as concentrators of external induced stresses. The formation of enriched ore shoots at these structural nodes can be explained by the suction-pumping of oreforming fluids by pipe-like (tubular) conduits under oriented stress. The deformation of K-feldsparthic rocks and albitites under stresses exceeding the elastic limit raised their fracture permeability due to cataclasis and brecciation and created favorable conditions for circulation of mineralizing fluids and precipitation of minerals. The use of tectonophysical modeling for the reconstruction of paleotectonic and fluid flow conditions during formation of hydrothermal mineralization allows a more precise evaluation of ore potential in deep levels and flanks of ore deposits.

ВОЗДЕЙСТВИЕ ПРИРОДНЫХ И АНТРОПОГЕННЫХ ФАКТОРОВ НА ЭЛЕМЕНТНЫЙ СОСТАВ РАСТЕНИЙ БАШКИРСКОГО ЗАУРАЛЬЯ

Рассмотрены особенности аккумуляции химических элементов в растениях фоновых и антропогенно нарушенных природно-территориальных комплексов (ПТК) Башкирского Зауралья по результатам исследований 1998–2014 гг. на модельных площадях, расположенных в фоновых ПТК, в естественных геохимических аномалиях Красноуральско-Сибай-Гайской рудоносной зоны и в антропогенно загрязненных ПТК на различном удалении от объектов горнорудного производства. Дана детальная характеристика накопления S и тяжелых металлов (ТМ) – Cu, Zn, Fe, Pb, Cd, Ni, Co, Cr и Mn – в почвах и анализ изменчивости концентрации подвижных форм за пятнадцать лет. Особое внимание уделено концентрации ТМ в укосах надземной биомассы и индикаторных видах растений Artemisia austriaca Jack., Salvia stepposa Sсhost., Thymus marschallianus Willd., Veronica incana L., Caragana frutex L., Phlomis tuberosa L., Achilea setacea Waldst. et Kit., Gallium verum L. Показаны различия в аккумуляции ТМ растениями различных агроботанических групп – злаков, разнотравья, бобовых, осок, ветоши. На основе сопряженного анализа содержания подвижных форм ТМ в почвах и в индикаторных видах растений продемонстрирована определяющая роль ландшафтногеохимических факторов в накоплении ТМ в биомассе. Рассмотрена изменчивость химического состава растений под воздействием погодных условий. Отмечено отсутствие прямой корреляции между содержанием подвижных форм ТМ в почвах и уровнем их концентрации в растениях и наличие временного сдвига в одиндва года в ходе их изменений. На основе расчета коэффициентов биологического поглощения составлены ряды видов-концентраторов ТМ, рекомендованных для оценки с помощью биоиндикации техногенной трансформации ландшафтов.

First data on the chemical composition and morphology of gold in the Tuba Kain deposit (South Urals)

926 The Tuba Kain deposit discovered in the early 20th century is located in the southwestern part of the Eastern Baymak ore-bearing zone confined to the western slope of the Magnitogorsk megastructure of the Southern Urals (Fig. 1). The ore field is composed of volcanogenic and volcano-sedimentary rocks of the Devonian Irendyk, Yarlykap, and Ulutau formations intruded by subvolcanic bodies of dacite porphyrites [1–3]. The rocks of the Eifelian Irendyk Formation distributed in the northwestern and central parts of the ore field are represented by lapilli and agglomerate tuffs of mixed composition with subordinate intercalations of gravel to psammitic tuffs. The lithological– petrographic composition of rock fragments is highly variable imparting variegated coloration to rocks: quartzites, hematite–quartz varieties, quartz porphyries, amygdaloid basalt porphyrites, and diorites. The overlying cherts of the Upper Eifelian Yarlykap Formation are approximately coeval with the Karamyltash Formation and Bugulygyr Horizon of the eastern areas. The rocks of the Givetian–lower Frasnian Ulutau Formation are developed in the western and southern parts of the ore field. The rock composition is relatively uniform with the dominant share of tuffstones and, less commonly, tuffaceous siltstones. The subvolcanic bodies occurring in the central, northern, and eastern parts of the ore field are represented by massive compact plagioclase and hornblende–plagioclase andesite–dacite and dacite porphyrites. At the beginning of the Tuba Kain deposit exploitation, it represented a submeridional gold–barite vein up to 5 m thick occurring among foliated rocks. The vein became exhausted and the residual ore-bearing complex is now represented by secondary quartzites with tourmaline and chlorite–sericite–quartz metasomatites. Their composition is as follows (wt %): SiO 2, 26.74–58.38; TiO 2, 0.35–0.76; Al 2O3, 8.41– 12.18; F 2O3, 7.28–10.06; MnO, 0.0; MgO, 3.93–4.15; CaO, 0.12–0.16; Na 2O, 2.38–2.55; K 2O, 1.24–2.92; P2O5, 0.02–0.11; S tot , 0.32–5.02; Ba, 1.59–28.05; Zn, 0.0051–0.0218; Cr, 0.0–0.0092; V, 0.0142–0.170; Sr, 0.0023–0.0634; Zr, 0.0076–0.0270. The rocks confined usually to contacts of subvolcanic dacite porphyrites are characterized by the following composition (wt %): SiO 2, 69.91; TiO 2, 0.36; Al 2O3, 14.02; F2O3, 3.84; MnO, 0.05; MgO, 1.87; CaO, 1.54; Na 2O, 4.87; K 2O, 0.09; P 2O5, 0.08; S tot , 0.01; Ba, 00233; Zn, 0.0011; Cr, 0.0011; Ni, 0.0085; V, 0.0003; Sr, 0.0306; Zr, 0.0148, Nb, 0.0011; Rb, 0.0010. These rocks are accompanied by tuffs of the Irendyk and Ulutau formations with mixed compositions (wt %): SiO 2, 59.09–67.86; TiO 2, 0.32–0.45; Al 2O3, 11.91–19.23; F2O3, 2.05–5.24; MnO, 0.02–0.13; MgO, 2.19–5.39; CaO, 0.11–2.71; Na 2O, 1.10–4.26; K 2O, 1.80–3.63; P2O5, 0.05–0.10; S tot , 0.06–1.15; Ba, 0.57–9.51; Zn, 0.0069–0.0596; Cr, 0.0015–0.0110; Ni, 0.0005– 0.0032; V, 0.0024–0.0081; Sr, 0.0027–0.0620; Zr, 0.0112–0.0245; Nb, 0.0006–0.0010; Rb, 0.0012–

AUTOMATED DRILL CORE LOGGING USING VISIBLE AND NEAR-INFRARED REFLECTANCE SPECTROSCOPY: A CASE STUDY FROM THE OLYMPIC DAM IOCG DEPOSIT, SOUTH AUSTRALIA

Reflectance spectrometers with automated scanning capabilities can gather compositional information directly from the surface of drill core. To showcase the usefulness of this analytical technique, 300 m of drill core from the Olympic Dam iron oxide copper-gold (IOCG) deposit, South Australia, were scanned using HyLogger. The reflectance spectra (400–2,500 nm) were analyzed to identify hematite and phengite, which are the most important alteration minerals at Olympic Dam. The results were plotted as a function of depth to produce a log that accurately identified ore-bearing and barren rocks. The position of the most intense absorption feature between 850 and 970 nm was found to correspond to iron concentration, and the intensity of the most intense absorption feature between 2,190 and 2,230 nm was found to correspond to aluminum concentration. In addition, phengite located near the ore-bearing zone was found to contain more aluminum than phengite located in the barren rocks, and this difference in phengite mineral chemistry was observable in the reflectance spectra between 2,190 and 2,230 nm.

Hydrothermal alteration and sulfide mineralization in gabbroids of the Markov Deep (Mid-Atlantic Ridge, 6° N)

A new type of sulfide occurrence related to metasomatically altered brecciated gabbroids has been studied at the Sierra Leone site situated in the axial rift valley of the Mid-Atlantic Ridge (Markov Deep, 6° N). Two associations of plutonic, subvolcanic, and volcanic rocks were dredged: (1) mid-ocean ridge basalts (MORB) and their intrusive analogues and (2) rocks of the silicic Fe-Ti-oxide series with dominating gabbronorites and sporadic trondhjemites. Almost all igneous rocks at the Sierra Leone site are enriched in Pb, Cu, U, Ga, Ta, Nb, Cs, and Rb and depleted in Zr, Th, and Hf. The rocks of the Fe-Ti-oxide series are enriched in Zn, Sn, and Mo and depleted in Ni and Cr. The main ore-bearing zone is situated at the foot of the eastern wall of the deep, where it is hosted in cataclastic hornblende gabbro and gabbronorite of the Fe-Ti-oxide series. Ore mineralization in metasomatically altered rocks is composed of quartz-sulfide and prehnite-sulfide veinlets, disseminated sulfide, and veined copper sulfide ore. The ore consists of pyrite, chalcopyrite, sphalerite, pyrrhotite, bornite, chalcocite, and digenite. The δ34S value of sulfides varies from 3.0 to 15.3‰. At the foot of the eastern wall of the Markov Deep, directly downslope from the ore-bearing zone, loose sediments contain grains of native Cu, Pb, Zn, and Sn and intermetallic compounds (isoferroplatinum, tetraferroplatinum, and brass) apparently derived from the ore. Mineral assemblages of ore-bearing metasomatic rocks and fluid inclusions therein were studied. Ore metasomatism developed under a low oxygen potential within a temperature interval from 400 to 160°C, though initial hydrothermal alteration of rocks proceeded at temperatures of 800–450°C. The temperature of stringer-disseminated ore mineralization is estimated at 170–280°C. The hydrothermal fluids are considered to be of magmatic origin; as the hydrothermal system evolved, they became diluted with seawater that was contained in fractured oceanic crust. The ore matter could have been derived from magmatic fluids that were released from water-saturated melts of the Fe-Ti oxide series during their ascent and leached from host gabbroids in the process of metasomatic alteration.

Hydrothermal Cu-Ni-Au-Ag mineralization in a granodiorite sill north of Cradock, Republic of South Africa

An undulating sheet-like granodiorite body is intrusive into sedimentary rocks and dolerite of the Karoo Supergroup north of Cradock. The top of this sheet, where in contact with dolerite, is characterised by the presence of graphite containing nodules of sedimentary origin, and by sulphide-arsenide mineralization. REE and other geochemical evidence indicate that the granodiorite and the ore-bearing horizon are genetically related, but the latter is more altered by hydrothermal fluids. Similarities in REE distribution patterns also imply very little assimilation of sedimentary material. The granodiorite displays plume-like features signifying that the material was plastic or semi-molten when segregation of the plume-like features took place. The Ni-mineralisation in the ore-bearing horizon is not linked to the MgO or Fe2O3 of the granodiorite or of the ore-bearing zone, and is regarded as a separate event of hydrothermal origin.

A fluid inclusion study of Au-W stratiform mineralization at Orlik near Humpolec, Czechoslovakia

Gold-scheelite mineralization occurs in polyphase, high-grade metamorphic rocks of the Moldanubicum in the core of the Bohemian Massif near the contact with the Variscan Central Moldanubian plution in SE Bohemia. The stratiform ore-bearing zone is cross-cut by younger pegmatite veins of Variscan age. Fluid inclusions were studied by microthermometry and micro-Raman analysis in quartz, apatite and scheelite. H 2 O-CO 2 fluids (CO 2 2 kbar to <1 kbar) and input of a new fluid (CH 4 -rich) along the tectonically weakened zone. Crystallization of scheelite (at T 360-390 o C and P<0.7 kbar) was probably caused by the change of oxidation state (CO 2 to CH 4 ) in the ore-bearing zone. The precipitation of gold and maldonite (Au 2 Bi) occurred after scheelite crystallization at temperatures lower than 373 o C (the upper thermal stability of maldonite)

Petrographic and geochemical evidence for a hypogene origin of granite-hosted, vein-type Mn mineralization at the New Ross Mn deposits, Lunenburg County, Nova Scotia, Canada

The New Ross Mn deposits consist of two centers of past mining activity located in the 370 Ma South Mountain batholith 10 km north of New Ross, Lunenburg County. The deposits occur as Mn oxide veins and lenses formed along steeply dipping northeast-trending faults. Previous investigators disagree as to whether the most economically important Mn oxides, pyrolusite and manganite, are of supergene or hypogene origin. Recent diamond drilling and geologic mapping have provided new data that support a hypogene origin.The South Mountain batholith in the area of the deposits consists mostly of coarse-grained megacrystic biotite monzogranite. A swarm of small, elongate leucomonzogranite plutons both intrude and are in fault contact with the monzogranite to the north and west of the deposits and at depth below one of the mine workings. These plutons are elongate parallel to a series of persistent northeast-trending topographic linears, which appear to represent faults and/or shear zones. This spatial association suggests that these structures played a role in the emplacement of the plutons. Brecciation and hydrothermal alteration of the leucomonzogranite plutons indicates that movement and hydrothermal activity continued on the faults after final crystallization of the plutons.Several types of hydrothermal alteration are well developed in the faults hosting the Mn mineralization and along several other northeast-trending structures in this region. The diamond drilling shows that, although the Mn mineralization is absent at depth, the fault zone and hydrothermal alteration persist to at least 452 m below the mine workings. Low-temperature hematization and argillic alteration is best developed within the main ore-bearing zone from surface to a depth of about 150 m. With increasing depth, the amount of argillic alteration decreases but hematization remains well developed. Desilicification (episyenitization) accompanied hematization at several localities in the megacrystic monzogranite and the leucomonzogranite intrusions. The desilicification is developed to the point that no primary quartz remains in the rock. Higher temperature alterations such as silicification, greisenization, K feldspathization, and albitization were caused by emplacement of the leucomonzogranite. The silicification occurs as total replacement of the rock and grades through greisenized selvages into unaltered leucomonzogranite or monzogranite. Textural evidence indicates that precipitation of carbonate minerals occurred prior to, during, and after crystallization of the Mn and Fe oxides.The activity of phosphate during the alteration sequences is of particular importance. Below the mine, P 2 O 5 enrichment occurs in the higher temperature silicified, greisenized, K feldspathized, and albitized rocks (up to 5.20 wt % P 2 O 5 ) and is manifest as abundant secondary fluorapatite. Phosphate remained present in the hydrothermal fluid at lower temperatures and resulted in crystallization of fluorapatite with Mn and Fe oxides in the mineralized zones and formation of a 1.2-m-wide quartz-fluorapatite-manjiroite vein (9.95 wt % P 2 O 5 ). Samples of manganite and pyrolusite often contain vug fillings and inclusions of rhodochrosite and minor amounts of other hypogene minerals such as knebelite and pinakiolite. Furthermore, these samples also contain anomalous amounts of Be (90 ppm), W (140 ppm), Mo (28 ppm), Pb (3,000 ppm), and Cu (1,500 ppm) which is consistent with their formation from fluids derived from a magmatic source. These textural relations and geochemical signatures indicate that the alteration sequence and Mn oxides, including those that were previously mined, could all be part of an evolving hydrothermal system developed in upwelling hydrothermal fluids. These processes operated along other northeast-trending faults throughout much of this region of the South Mountain batholith, which suggests a high potential for as yet undiscovered deposits of Mn and other granophile elements.

Disseminated tin mineralization in the roof of the Bushveld granite pluton at the Zaaiplaats Mine, with implications for the genesis of magmatic hydrothermal tin systems

The Bobbejaankop Granite is a hydrothermally altered facies equivalent of the typical Bushveld (Nebo) granite. On a regional scale, the Bobbejaankop usually occurs in the upper part of the sheetlike Nebo pluton, but it is particularly well developed in a roof cupola at the Zaaiplaats tin mine. Several styles of endogranitic tin mineralization occur at the Zaaiplaats mine, but disseminated deposits hosted by the Bobbejaankop Granite form the main producing ores.Cassiterite, commonly associated with scheelite and sulfides, is interstitial to the major silicate minerals in the disseminated ores. The ores are confined to a favorable zone that can be defined on geochemical-statistical grounds as a tabular body of varying thickness (55-66 m) with an upper contact that is parallel to, and some 66 to 83 m below, the pluton roof contact. Geochemical halos around the ore-bearing zone are absent or poorly developed and, except for the anomalous tin contents in this zone, there are few obvious differences between mineralized and barren Bobbejaankop Granite.The Zaaiplaats rocks are more heavily altered than equivalent granites in the southeastern Bushveld Complex, and granite in the disseminated tin zone is more altered than barren Bobbejaankop Granite. A complex history of sequential alteration can be recognized, beginning with high-temperature feldspathic (albitization and microclinization) alterations and followed by chloritization, sericitization, and lastly, silicification. These events induced many chemical changes. Compared with Bobbejaankop variants in the southeastern Bushveld, the entire Zaaiplaats suite is enriched in K, Ca, Rb, Cu, and Sn, and depleted in Na. Within the mine area, granite from the mineralized zone contains higher Na, Sn, W, As, S, and F, but lower K and Rb contents than the barren granite. These differences reflect increasing degrees of fluid-controlled precipitation and alteration.For the most part, the Bushveld granites are not metallogenically specialized in the manner of other tin mineralized plutons. Ore genesis cannot be explained by geochemical heredity, or contamination during or after emplacement. Fractional crystallization cannot directly produce significant tin concentrations; the Bushveld magma contained relatively low (

Effects of Uranium Mining on Groundwater in Ambrosia Lake Area, New Mexico: ABSTRACT

The principal ore-bearing zone in the Ambrosia Lake area of the Grants uranium district is the Westwater Canyon Member of the Morrison Formation of Jurassic age. This is also one of the major artesian aquifers in the region. Significant declines in the potentiometric head within the aquifer have been recorded, and digital modeling shows that declines may locally approach 3,000 ft (900 m) in the vicinity of a mine. Loss of potentiometric head in the Westwater Canyon Member has resulted in the interformational migration of groundwater along fault zones from overlying aquifers of Cretaceous age. This has resulted in local deterioration in chemical quality of the groundwater. End_of_Article - Last_Page 690------------

Analysis and Distribution of Packing Properties in Sand-Sized Sediments: 2. The Distribution of the Packing Measurements and an Example of Packing Analysis

Packing analysis is performed on the three sedimentary-rock types-the arkose, graywacke, and quartz-ite. It is shown, by means of analysis of variance, that there are no significant differences among packing-proximity and packing-density measurements for the three rock types. By means of covariance and regression analyses, the interdependency of the variables-packing density, packing proximity, and intercept size-is established. An example of the utility of packing as a geologic tool is presented. It is shown that an ore-bearing zone and a barren zone, from the Salt Wash member of the Morrison formation, can be differentiated on the basis of packing proximity. This difference is manifested as a clustering effect. A possible cause of this effect is discussed. Finally, it is suggested that packing analysis be included in future sedimentary-rock analysis.

CONTROL OF ORE BY PRIMARY IGNEOUS STRUCTURES, PORCHER ISLAND, BRITISH COLUMBIA

The ore deposits at Surf Point and Edye Pass Mines, Porcher Island, British Columbia, lie in a quartz diorite stock. They are a series of auriferous quartz-pyrite veins occurring in a N. 20°E. zone along the axis of an arch of flow layers. Strong N. 30°E. shears in an adjacent to the stock aided in the enlargement of the magma chamber. The same stresses acting in the arch formed the ore-bearing structures by a series of small transverse movements involving the primary joints. Study of the internal structures gave valuable information on the form of the stock and the extension of the ore-bearing zone.