Tons Of Gold Research Articles

The origin and evolution of the Klondike goldfields, Yukon, Canada

The world famous Klondike goldfields are located in the unglaciated part of west-central Yukon, Canada. Since their discovery over 100 years ago, they have produced an estimated 311 tonnes of gold, primarily from bench and creek placers that are fluvial in origin and range from Pliocene to Holocene in age. Historically, the placers are classified into three levels of gravel with four main units. These include the high-level White Channel Gravel (Pliocene), presently the most important gold-bearing unit, which sits nonconformably on an erosional bedrock surface (i.e., the ‘White Channel strath’) and is overlain and interbedded with the glaciofluvial Klondike Gravel (Pliocene); the intermediate-level gravel (Pleistocene), the least important economically; and the low-level gravel (Pleistocene–Holocene), historically the most important gold-bearing unit, but it has been mined three or four times now. The goldfields originated from the weathering and erosion of early Cretaceous, discordant mesothermal quartz veins, and the light grey color of the matrix of the White Channel Gravel is due mainly to weathering and diagenetic alteration by groundwater flow. The concentration of placer gold is related to a hierarchy of physical scales: at the lithofacies scale (metres), bed roughness determined sites of gold deposition; at the element scale (tens of metres), gravel bars were preferentially enriched in gold; at the reach scale (hundreds of metres), stream gradient was an important factor; at the system scale (hundreds of km), braided river environments transported large amounts of gold; and at the sequence scale (thousands of km), economic placers formed initially in the high-level White Channel Gravel and later in the intermediate-level and low-level gravel. The White Channel strath is interpreted as an erosional ‘tectonic’ terrace that formed during isostatic uplift and under conditions of dynamic equilibrium. The high-level White Channel Gravel and Klondike Gravel are interpreted as a depositional ‘climatic’ terrace that formed during a reversal in the tectonically induced downcutting, which is attributed to the initial and most extensive of the pre-Reid glaciations (∼3 Ma) in the Yukon. The intermediate-level gravel is interpreted as minor erosional ‘complex response’ terraces that formed during static equilibrium when there were pauses in valley-floor degradation, which are attributed to the subsequent and less extensive pre-Reid glaciations. The low-level gravel formed also during valley-floor degradation and may represent a return to dynamic equilibrium conditions. Hence, the dominant forcing mechanisms controlling the evolution of the goldfields were isostatically compensated exhumation and climatic change related to the repeated glaciation of the Yukon. In addition, the lowering of baselevel from high-level, to intermediate-level and finally to low-level gravel was accompanied by a decrease in accommodation space (as indicated by a decrease in gravel thickness), which resulted in an increase in the concentration of the placer gold.

The development of volcanic hosted massive sulfide and barite–gold orebodies on Wetar Island, Indonesia

Wetar Island is composed of Neogene volcanic rocks and minor oceanic sediments and forms part of the Inner Banda Arc. The island preserves precious metal-rich volcanogenic massive sulfide and barite deposits, which produced approximately 17 metric tonnes of gold. The polymetallic massive sulfides are dominantly pyrite (locally arsenian), with minor chalcopyrite which are cut by late fractures infilled with covellite, chalcocite, tennantite–tetrahedrite, enargite, bornite and Fe-poor sphalerite. Barite orebodies are developed on the flanks and locally overly the massive sulfides. These orebodies comprise friable barite and minor sulfides, cemented by a series of complex arsenates, oxides, hydroxides and sulfate, with gold present as <10 μm free grains. Linear and pipe-like structures comprising barite and iron-oxides beneath the barite deposits are interpreted as feeder structures to the barite mineralization. Hydrothermal alteration around the orebodies is zoned and dominated by illite–kaolinite–smectite assemblages; however, local alunite and pyrophyllite are indicative of late acidic, oxidizing hydrothermal fluids proximal to mineralization. Altered footwall volcanic rocks give an illite K–Ar age of 4.7±0.16 Ma and a 40Ar/39Ar age of 4.93±0.21 Ma. Fluid inclusion data suggest that hydrothermal fluid temperatures were around 250–270°C, showed no evidence of boiling, with a mean salinity of 3.2 wt% equivalent NaCl. The δ34S composition of sulfides ranges between +3.3‰ and +11.7‰ and suggests a significant contribution of sulfur from the underlying volcanic edifice. The δ34S barite data vary between +22.4‰ and +31.0‰, close to Miocene seawater sulfate. Whole rock 87Sr/86Sr analyses of unaltered volcanic rocks (0.70748–0.71106) reflect contributions from subducted continental material in their source region. The 87Sr/86Sr barite data (0.7076–0.7088) indicate a dominant Miocene seawater component to the hydrothermal system. The mineral deposits formed on the flanks of a volcanic edifice at depths of ~2 km. Spectacular sulfide mounds showing talus textures are localized onto faults, which provided the main pathways for high-temperature hydrothermal fluids and the development of associated stockworks. The orebodies were covered and preserved by post-mineralization chert, gypsum, Globigerina-bearing limestone, lahars, subaqueous debris flows and pyroclastics rocks.

Geological and Geochemical Characteristics of the Zhulazhaga Gold Deposit in Inner Mongolia, China

Abstract Located in Alxa Zuoqi (Left Banner) of Inner Mongolia, China, the Zhulazhaga gold deposit is the first large‐scale gold deposit that was found in the middle‐upper Proterozoic strata along the north margin of the North China craton in recent years. It was discovered by the No. 1 Geophysical and Geochemical Exploration Party of Inner Mongolia as a result of prospecting a geochemical anomaly. By now, over 50 tonnes of gold has been defined, with an average Au grade of 4 g/t. The ore bodies occur in the first lithological unit of the Mesoproterozoic Zhulazhagamaodao Formation (MZF), which is composed mainly of epimetamorphic sandstone and siltstone and partly of volcanic rocks. With high concentration of gold, the first lithological unit of the MZF became the source bed for the late‐stage ore formation. Controlled by the interstratal fracture zones, the ore bodies mostly appear along the bedding with occurrence similar to that of the strata. The primitive ore types are predominantly the altered rock type with minor ore belonging to the quartz veins type. There are also some oxidized ore near the surface. The metallic minerals are composed mainly of pyrite, pyrrhotite and arsenopyrite with minor chalcopyrite, galena and limonite. Most gold minerals appear as native gold and electrum. Hydrothermal alterations associated with the ore formation are actinolitization, silicatization, sulfidation and carbonation.A total of 100 two‐phase H2O‐rich and 7 three‐phase daughter crystal‐bearing inclusions were measured in seven gold‐bearing quartz samples from the Zhulazhaga gold deposit. The homogenization temperatures of the two‐phase H2O‐rich inclusions range from 155 to 401°C, with an average temperature of 284°C and bimodal distributions from 240 to 260°C and 300 to 320°C respectively. The salinities of the two‐phase H2O‐rich inclusions vary from 9.22wt% to 24.30wt% NaCl equiv, with a mode between 23wt% and 24wt% NaCl equiv. Comparatively, the homogenization temperatures of the three‐phase daughter crystal‐bearing inclusions vary from 210 to 435°C and the salinities from 29.13wt% to 32.62wt% NaCl equiv. It indicates that the ore‐forming fluid is meso‐hypothermal and characterized by high salinity, which is apparently different from the metamorphic origin with low salinity. It suggests a magmatic origin of the gold‐bearing fluid.The δ18O values of quartz from auriferous veins range from 11.9 to 16.3 per mil, and the calculated δ18O values in equilibrium with quartz vary from 1.06 to 9.60 per mil, which fall between the values of meteoric water and magmatic water. It reflects that the ore‐forming fluid may be the product of mixing of meteoric water and magmatic water. Based on geological and geochemical studies of the Zhulazhaga gold deposit, it is supposed that the volcanism in the Mesoproterozoic might make gold pre‐concentrate in the strata. The extensive and intensive Hercynian tectono‐magmatic activity not only brought along a large number of ore‐forming materials, but also made the gold from the strata rework. It can be concluded that the ore bodies were mainly formed in late hydrothermal reworking stage. Compared with typical gold deposits associated with epimetamorphic clastic rocks, the Zhulazhaga deposit has similar features in occurrence of ore bodies, ore‐controlling structure, wall‐rock alterations and mineral assemblages. Therefore, the Zhulazhaga gold deposit belongs to the epimetamorphic clastic rock type.

Episodic meteoric water interaction in a granite-hosted hydrothermal gold-silver system: Geochemistry of fluids at the Mugeuk mine, South Korea

The Mugeuk mine was historically the largest gold-silver producer in South Korea, and yielded more than ten metric tons of gold from ores with an average grade of about 8 g/ton Au and Au/Ag ratios near 1:5. Ore deposits consist of >10 subparallel quartz-calcite veins (typically 0.6 to 1.0 m wide) that fill faults and fractures in Jurassic granodiorite and Cretaceous quartz porphyry. Veins formed during six successive hydrothermal events of Late Cretaceous age. Ore mineralogy of the veins is complex, consisting mainly of pyrite and base-metal sulfides with electrum (23‐51 atom. % Au), native silver, argentite and silver sulfosalts (polybasite, pyrargyrite). Stage I veins contain no gold and silver (e.g., barren). During stages II to V, economic quantities of gold and silver were precipitated. Stages III and IV represent the culmination of gold precipitation in distinct sulfide bands, whereas stage V represents a shift to dominantly silver deposition. Stage VI veins are barren post-ore quartz-calcite-fluorite. A variety of types of geochemical data indicate that deposition of gold and silver resulted mainly from cooling of ore fluids, accompanying successive incursions of meteoric water into the hydrothermal system. Fluid inclusion data show general decreases of temperature and salinity within each stage. Ore mineral assemblages indicate decreases in the fugacity of sulfur with decreasing temperatures during the deposition of gold and silver. Measured and calculated δ 18 O values of hydrothermal fluids decrease generally from +3.0 to ‐7.4‰ from stages II through VI, and δD values range from ‐66 to ‐84‰. The Au-Ag deposits at Mugeuk, in particular their mineralogy, Au/Ag ratios and fluid geochemistry, are the result of episodic meteoric water events within the granite-hosted hydrothermal system. Early stages of the hydrothermal history involved successive introduction of new pulses of meteoric ore fluids, each of which equilibrated with the host granitic rocks at successively higher water-to-rock ratios and lower temperatures during deposition of gold-silver mineralization. Later stages were the result of inundation of the hydrothermal system by isotopically unevolved meteoric waters, resulting in a silver-rich overprint on the earlier gold-silver system.

Paleoproterozoic high-sulfidation mineralization in the Tapajós gold province, Amazonian Craton, Brazil: geology, mineralogy, alunite argon age, and stable-isotope constraints

The Brazilian Tapajós gold province contains the first evidence of high-sulfidation gold mineralization in the Amazonian Craton. The mineralization appears to be in large nested calderas. The Tapajós–Parima (or Ventuari–Tapajós) geological province consists of a metamorphic, igneous, and sedimentary sequence formed during a 2.10 to 1.87 Ga ocean−continent orogeny. The high-sulfidation mineralization with magmatic-hydrothermal alunite is related to hydrothermal breccias hosted in a rhyolitic volcanic ring complex that contains granitic stocks ranging in age from 1.89 to 1.87 Ga. Cone-shaped hydrothermal breccias, which flare upward, contain vuggy silica and have an overlying brecciated cap of massive silica; the deposits are located in the uppermost part of a ring-structure volcanic cone. Drill cores of one of the hydrothermal breccias contain alunite, natroalunite, pyrophyllite, andalusite, quartz, rutile, diaspore, woodhouseite–svanbergite, kaolinite, and pyrite along with inclusions of enargite–luzonite, chalcopyrite, bornite, and covellite. The siliceous core of this alteration center is surrounded by advanced argillic and argillic alteration zones that grade outward into large areas of propylitically altered rocks with sericitic alteration assemblages at depth. Several occurrences and generations of alunite are observed. Alunite is disseminated in the advanced argillic haloes that envelop massive and vuggy silica or that underlie the brecciated silica cap. Coarse-grained alunite also occurs in branching veins and locally is partly replaced by a later generation of fine-grained alunite. Silicified hydrothermal breccias associated with the alunite contain an estimated reserve of 30 tonnes of gold in rock that grades up to 4.5 g t −1 Au. Seven alunite samples gave 40Ar/ 39Ar ages of 1.869 to 1.846 Ga, with various degrees of apparent minor Ar loss. Stable isotopic data require a magmatic-hydrothermal origin for the alunite, typical for high-sulfidation mineralization. The δ 34S values of most samples of alunite range from 14.0‰ to 36.9‰. Sulfur isotopic alunite–pyrite and oxygen isotopic alunite SO 4−OH temperatures range from 130 to 420 °C. The δD H 2O and δ 18O H 2O values for alunite-forming hydrothermal fluids suggest a predominance of magmatic water, with a small meteoric contribution. A rare sample of supergene alunite has a δ 34S value of 4.1‰ and an 40Ar/ 39Ar age of 51.3±0.1 Ma. Other than local foliation in the volcanic rocks and recrystallization of alunite near faults, the mineralization and associated alteration appears to have been remarkably undisturbed by later metamorphism and by supergene alteration. The Au mineralization was preserved because of burial by sediments and tuffs in taphrogenic basins that probably developed shortly after mineralization and were probably first exhumed at about 60 Ma. Because high-sulfidation mineralization forms at relatively shallow crustal levels, the discoveries in Tapajós province provide new perspectives for mineral exploration for the Amazonian and perhaps for other Precambrian cratons.

Cypress Beams, Kufic Script, and Cut Stone: Rebuilding the Master Narrative of European History

In the year 769 a crisis appeared likely to engulf the Japanese imperial court at Nara. The empress Shotoku, aged fifty-two and childless, indeed never married, gave many signs that she intended to appoint a Buddhist priest named Dokyo as her successor. A noted faith healer, Dokyo was credited with curing the empress of a serious illness, for which she rewarded him with a succession of high offices in the imperial bureaucracy. That he was looked upon with favor by the empress was thus no secret, but there may have been more to their relationship than a magical cure and political rewards. One source from a few decades later says flatly that the two of them shared the same pillow. Dokyo had, in any case, arrived almost to the pinnacle of Japanese power, and yet there stood between him and the very top the inescapable fact that he was a commoner.1 Apart from any personal feelings for Dokyo, Shotoku had a long history of favoring the progress of Buddhism in her country. In this she was following the inclinations and policies of her father, Emperor Shomu, who, for example, decreed that every province must build and maintain an official Buddhist temple, where ceremonies would be carried out on a regular basis and where statues and sutras would be kept and accorded due honor. It was Shomu, moreover, who launched the project for erecting a massive gilded bronze statue of Buddha; its construction consumed over three hundred tons of copper and sixteen tons of gold. The temple enclosing it is the world's largest wooden structure. Before the statue was com pleted, though, Shomu abdicated in favor of his daughter in order to pursue his desire to become a Buddhist priest. She took the name Koken at the start of what turned out to be for her the first of two reigns, and she issued an edict declaring the name of the new era to be Heavenly Peace and Victorious Buddhism. Within a few years the great statue was completed, and she had it dedicated in what is

Auriferous mineralizations in the Murgul-Artvin-Maradit area northeastern Turkey

The auriferous mineralizations, as the subject of this paper, are placed in the Murgul, Artvin and Maradit surroundings, in the extreme northeastern part of the Turkey. The area is between Black Sea coast to the northwest and Coruh river to the east, northerly bordered by the Georgian - Turkish border and by the Artvin - Fýndýklý line to the south, including spring of the Murguldere. The field is made up of volcanic, volcanic-sedimen- tary, sedimentary and granitoid formations, from Jurassic to Quaternary time. In that period numerous composite petrogenetic complexes had been formed. The oldest is volcanic and volcanic-sedimentary complex including vol- canic rocks of andesitic or intermediate-acidic character, Jurassic in age. They are accompanied by the Iskalka koprusu and Budiyet koprusu copper mineralizations. Gold in this complex has not been studied yet. This rock assemblage is overlain by the acidic rhyolitic and rhyodacitic volcanic and volcanic-sedimentary complex, asso- ciated with large copper deposits and a large number of still not explored or partly investigated copper occur- rences, formed during the Upper Jurassic - Lower Cretaceous. The gold-bearing, related to this complex, is not distinctly developed. According to the present knowledge, precious metals as trace elements are registered in copper deposits in the Murgul surroundings (Anayatak, Cakmakkaya, Aduca dere, Kilise tepe etc), then in the Artvin vicinity (Kuvarshan, Irsa Maden, Sinkot, Seyitler and Umasen). The similar gold and silver appearances are to be expected in the other copper mineralizations, particularly in the Hopa circles (Peronot, Sivrikaya, Kutunit and others). These copper occurrences and deposits are characterized by relatively low gold grades (mostly less than 0.5 ppm) and variable silver contents, with locally high grades (from traces to 180 ppm). However, if large copper reserves are taken into consideration, amounting more than 100 million tons, low grades became signifi- cant; at least 50 tons of gold and several hundred tons of silver is expected to be found. The next petrogenic complex was formed during the Upper Cretaceous - Paleogene time. This is a composite petrogenic unit, en- closing volcanic, volcanic-sedimentary and sedimentary formations. They represent a complete development, beginning from basalts and spilites, throughout andesites, to dacites and rhyolites. The most important rocks in this complex, bearing precious metals, associated with copper, zinc and lead mineralizations, are andesites, part- ly sediments, composed of re-deposited products of andesitic volcanism. In this petrogenic rock assemblage in the related metallogenic stage, two types of gold-bearing mineralizations are distinguished. These are the Akarþen, Hohur sýrtý and Madenkoy base metal deposit near Cayeli, with gold grading up to 11,43 ppm (in Madenkoy) and silver contents ranging from several tens grams per ton of ore up to 241 ppm, including even 350 ppm in Akarþen galena. In the same complex, including the potentially ore-bearing sediments, such as tuffaceous sandstones, contents of 0,11 ppm gold and 2,25 ppm silver have been found. To the next precious metals type belong mineralizations nearby Pehlivan koy near Maradit. They occur in the highly hydrothermally altered andesites, with pyrite and copper minerals. As a special alteration type, adularization is remarkable, indicating the epithermal copper origin and accompanying the gold mineralizations. In only one sample 0,72 ppm gold and 50 ppm silver were detected. These features indicate it as a special mineralization type. The third of auriferous mi- neralizations is found in the Melo dere ravine (Gorge) near Artvin. This is the quartzdiorite, Eocene in age, local- ly bearing high chalcopyrite concentrations, with low gold grades (up to 0,03 ppm), but with higher silver (7,2 ppm). As it is visible from the presented facts, the Murgul - Artvin - Maradit area is considered as very interesting for the gold-bearing copper, zinc and lead mineralizations.

TELLURIDE MINERALOGY OF THE GOLDEN MILE DEPOSIT, KALGOORLIE, WESTERN AUSTRALIA

The Golden Mile, Kalgoorlie, Western Australia, is a mesozonal gold deposit unusual because of its enormous size (>1,457 tonnes of gold) and because tellurides are responsible for approximately 20% of gold production. Gold mineralization is hosted primarily by Archean-aged dolerites and basalts that have been metamorphosed to the greenschist facies. This mineralization occurs in hundreds of auriferous and telluride-bearing lodes, which have been classified into three structural types on the basis of orientation: main (trending NNW), caunter (trending NW) and cross lodes (trending NE). Three distinct styles of hydrothermal mineralization are present in the deposit. The early Fimiston-style lodes are characterized by main, caunter and cross lodes. The Oroya-style lodes (V- and Te-rich) occur in later dilational jogs and veinlets within a shear zone. Both of these are overprinted by the younger Mount-Charlotte-style mineralization (quartz-vein stockwork). Nineteen tellurium-bearing minerals occur in the Golden Mile deposit. Calaverite, petzite, coloradoite, altaite and native gold are most common throughout the deposit, whereas tellurantimony, melonite, hessite, stutzite, krennerite and sylvanite are rare in the main and caunter lodes. In addition, hessite and montbrayite are found in trace amounts in the cross and main lodes, respectively. There is no systematic distribution of tellurides within a given lode. Tellurides in Fimiston-style ores formed at ca. 300° to 170°C during cooling of the deposit. Values of f (Te2) and f (S2) determined at 300°C on the basis of the stability of native elements, tellurides and sulfides, are ca. log f (Te2) in the range −11.4 to −6.8 and log f (S2) in the range −12.6 to −5.5. No spatial variations in the composition of native gold, tetrahedrite-group minerals and tellurides occur in the Golden Mile deposit, although there is a weak to moderate decrease in gold fineness with depth. Marked differences in telluride mineralogy in and between individual lodes likely reflect variations in physicochemical conditions during ore formation or mechanisms of precious-metal deposition.

War Crimes of the Deutsche Bank and the Dresdner Bank: Office of Military Government (U.S.) Reports

In November 1946, US Government financial experts inside former Nazi Germany concluded that Germany's most powerful banks must be liquidated if lasting peace was to be achieved. The giant Deutsche and Dredener Banks had completely intertwined themselves with the Nazi regime and were directly responsible for the systematic theft of Jewish property, slave labour, and financing the construction of SS concentration camps. As the Americans in the Finance Division of the Office of Military Government (US) -- OMGUS -- saw things at the time, the bank leaders should be tried as war criminals and barred from ever holding any positions of importance in German political or economic life. However, these recommendations were never implemented. In fact, many of the officials of the Deutsche Bank went on to be some of the most important figures in German economic development in the postwar period. The Deutsche Bank secretly retained almost a ton of gold taken from the dead at concentration camps; the Dresdener Bank re-emerged as a multinational financial giant. Meanwhile, the US Government buried the 500+ page report of its financial experts in classified files, where they gathered dust for decades. Today, the Deutsche Bank is the largest financial institution in the world and the Dresdener Bank is not far behind.

Mercury as a useful pathfinder for the Chinkuashih enargite-gold deposits, Taiwan

The Chinkuashih is a group of dacite-related hydrothermal enargite-gold deposits of the Quaternary age, which produced 94 tons of gold and 119,101 tons of copper from 1895 to 1987. It has remaining reserves of 656 tons of gold with an average grade range of 1.5–3.5 g/ton of Au for all orebodies discovered. Mercury content in different media such as stream sediments, heavy minerals in stream sediments, soils, rocks/ores, and pyrite samples was analyzed by a gold–film mercury detector to evaluate whether mercury is a good pathfinder for these types of deposits at Chinkuashih. The gold film technique is more rapid and cheaper than the traditional fire assay or fire assay/ICP-MS gold and trace element analyses. Mercury in stream sediments and soils indicated the border zone of gold mineralization 12 km away from the center of mineralization at Chinkuashih. Mercury in heavy minerals of the stream sediments distinguished the intermediate zone with gold veins and gold/gold–copper breccia pipes from the core or inner zone with the gold–copper zone. It has been found that contours of 1000 or 500 ppb Hg of soil samples can delineate the outcropping gold orebodies. The gold ores generally contain 1000 ppb or more Hg.

La explotación aurífera en el occidente asturiano: evolución histórica y situación actual

Western Asturias in the Spanish northwest has a long gold mining tradition that dates back to before the Roman conquest and has lasted, through ups and downs, into the present day. Mining is now coming back into its own due to Rio Narcea Gold Mines, whose intense digging brought up nearly three tons of gold in the year 2000, fundamentally in the towns of Belmonte and Salas. In addition to mining panning for gold is being revived as a source of the precious metal and a tourist attraction for the Navelgas area of the town of Tineo.

War crimes of the Deutsche Bank and the Dresdner Bank: Office of Military Government (U.S) Reports

In November 1946, US Government financial experts inside former Nazi Germany concluded that Germany's most powerful banks must be liquidated if lasting peace was to be achieved. The giant Deutsche and Dredener Banks had completely intertwined themselves with the Nazi regime and were directly responsible for the systematic theft of Jewish property, slave labour, and financing the construction of SS concentration camps. As the Americans in the Finance Division of the Office of Military Government (US) -- OMGUS -- saw things at the time, the bank leaders should be tried as war criminals and barred from ever holding any positions of importance in German political or economic life. However, these recommendations were never implemented. In fact, many of the officials of the Deutsche Bank went on to be some of the most important figures in German economic development in the postwar period. The Deutsche Bank secretly retained almost a ton of gold taken from the dead at concentration camps; the Dresdener Bank re-emerged as a multinational financial giant. Meanwhile, the US Government buried the 500+ page report of its financial experts in classified files, where they gathered dust for decades. Today, the Deutsche Bank is the largest financial institution in the world and the Dresdener Bank is not far behind.

Redbed-type gold mineralisation, Kupferschiefer, south-west Poland

A new type of gold mineralisation containing minor amounts of platinum and palladium has been found proximal to the secondary redox interface located below the Cu–Ag Kupferschiefer orebody of the Polkowice-Sieroszowice mine in the south-western part of the Lubin–Sieroszowice district, Poland. This deposit can be classified as redbed-type gold. Our study shows that gold, platinum and palladium occur in secondary red-coloured sections of the basal Zechstein sedimentary rocks and in the uppermost Weissliegendes sandstone. Noble metal mineralisation occurs within an average interval of 0.22 m, which lies directly below the copper ores. The average grade of the horizon is 2.25 ppm Au, 0.138 ppm Pt and 0.082 ppm Pd with a metal content of several tens of tonnes of gold. A transition zone has been recognised between the gold-bearing horizon and the copper deposit. This transition zone is characterised by the presence of low grades of copper ( 0.5 ppm). Native gold accompanied by electrum, mercury-bearing gold, haematite, covellite, chalcocite, bornite and chalcopyrite has been identified in the gold-bearing horizon. In some sections, Pd-arsenides, tetra-auricupride, Co-arsenides, clausthalite, tennantite, digenite, yarrowite, spionkopite and galena have also been noted.

Geology, distribution, and classification of gold deposits in the western Qinling belt, central China

Gold deposits of the western Qinling belt occur within the western part of the Qinling–Dabie–Sulu orogen, which is located between the Precambrian North China and Yangtze cratons and east of the Songpan–Ganzi basin. The early Paleozoic to early Mesozoic orogen can be divided into northern, central, and southern zones, separated by the Shangdan and Lixian–Shanyang thrust fault systems. The northern zone consists of an early Paleozoic arc accreted to the North China craton by ca. 450 Ma. The central zone, which contains numerous orogenic gold deposits, is dominated by clastic rocks formed in a late Paleozoic basin between the converging cratonic blocks. The southern zone is characterized by the easternmost exposure of Triassic sedimentary rocks of the Songpan–Ganzi basin. These Early to Late Triassic turbidities, in part calcareous, of the immense Songpan–Ganzi basin also border the western Qinling belt to the west. Carlin-like gold deposits are abundant (1) along a westward extension of the southern zone defined by a window of early Paleozoic clastic rocks extending into the basin, and (2) within the easternmost margin of the basinal rocks to the south of the extension, and in adjacent cover rocks of the Yangtze craton. Triassic and Early Jurassic synkinematic granitoids are widespread across the western Qinling belt, as well as in the Songpan–Ganzi basin. Orogenic lode gold deposits along brittle–ductile shear zones occur within greenschist-facies, highly-deformed, Devonian and younger clastic rocks of the central zone. Mainly coarse-grained gold, along with pyrite, pyrrhotite, arsenopyrite, and minor base metal sulfides, occur in networks of quartz veinlets, brecciated wall rock, and are disseminated in altered wall rock. Isotopic dates suggest that the deposits formed during the Late Triassic to Middle Jurassic as the leading edge of the Yangtze craton was thrust beneath rocks of the western Qinling belt. Many gold-bearing placers are distributed along the river systems that flow south from the lode-bearing central zone. Carlin-like gold deposits have only been identified during the last decade in the southern zone of the western Qinling and in the northeastern corner of the Songpan–Ganzi basin. The deposits mainly contain micron-diameter gold in arsenical pyrite; are characterized by the common occurrence of cinnabar, stibnite, realgar, and orpiment; exhibit strong silicification, carbonatization, pyritization, and decalcification dissolution textures; and are structurally controlled. The lack of reactive host lithologies may have prevented development of large (>100 tonnes of gold), stratigraphically-controlled orebodies, which are typical of the Carlin deposits in the western USA. These deposits are hosted by Triassic turbidities and shallow-water carbonates, and an early Paleozoic inlier in the Songpan–Ganzi basin that extends in an east–west belt for about 300 km. Rather than true "Carlin" deposits, these Carlin-like deposits may be some type of shallow-crustal (i.e., epithermal) hybrid with features intermediate to Nevada-style Carlin deposits and the orogenic gold deposits to the immediate north. These Carlin-like deposits also overlap in age with the early Mesozoic orogenic gold deposits and, therefore, also formed during the final stages of collision between the cratons and intermediate basin closure.

Nature, age, and tectonic setting of granitoid-hosted, orogenic gold deposits of the Jiaodong Peninsula, eastern North China craton, China

The Jiaodong gold province, along the southeastern margin of the North China craton, has combined production and resources of >900 tonnes of gold. More than 95% of the gold in this province is hosted in Mesozoic granitoids, which intruded Late Archean metamorphic basement rocks episodically at ca. 160–150 and 130–126 Ma. The deposits of the Jiaodong Peninsula form one of the largest provinces of granitoid-hosted lode-gold deposits in the world. The Jiaodong gold deposits occur as massive auriferous quartz veins hosted in subsidiary second- or third-order faults, and as disseminated- and stockwork-style mineralization hosted in alteration zones along major regional-scale faults. Mineralization took place during brittle reactivation (D3) of pre-existing D2 ductile shear zones. Wall rock alteration is dominated by K-feldspar and sericite, with also sulfide minerals and extensive silicification closest to the orebodies. The alteration was accompanied by the introduction of volatiles, Fe, Mg, K, Rb, Ag, As, Au, Bi, and Sb. Enrichment of base metals in the gold lodes is generally low, although locally significant. Gold deposition took place at temperatures of 250 to 350 °C for most gold deposits, and the ore fluids are CO2-bearing and have calculated salinities of 6–13 wt% NaCl equiv. Deposits from the Zhao–Ye, Xixia, and Muping–Rushan belts have similar, if not identical, structural controls, alteration patterns, ore mineral assemblages, and stable isotope signatures. Lead isotope data indicate that the ore-stage leads were buffered by their host rocks. The granitoid-hosted gold deposits in the Zhao–Ye belt are most radiogenic, the greenstone-hosted deposits in the Xixia belt is the least radiogenic and the granitoid-hosted deposits in the Muping–Rushan belt have intermediate compositions. Gold mineralization in the Zhao–Ye, Xixia, and Muping–Rushan belts in the Jiaodong gold province appears to be broadly contemporaneously at ca. 130–120 Ma, as constrained by SHRIMP U–Pb zircon dating on host rocks and a post-gold dike, as well as by Ar–Ar, Rb–Sr, and K–Ar dating of hydrothermal alteration minerals and ores. This Early Cretaceous age is about 100 million years younger than the peak of ultra-high pressure metamorphism in the Qinling–Dabie–Sulu orogen between the North China and Yangtze cratons, and about 500 km south of the gold province. However, it overlaps with the extension and exhumation stage of the collisional orogeny, and the subduction of the Pacific plate beneath the Eurasian continental crust. Whereas the majority of the Jiaodong gold deposits occur on the margin of the North China craton, some also occur in the suture zone between the two cratons. They are significantly landward relative to the subduction zone of the Pacific Plate compared with typical orogenic lode-gold deposits globally. Lode-gold deposits of ca. 130–120 Ma occurred on both sides of the Tan-Lu fault zone. Available data favor a temporal link of gold mineralization with Pacific Plate subduction.

The transition from porphyry- to epithermal-style gold mineralization at Ladolam, Lihir Island, Papua New Guinea: a reconnaissance study

The exceptionally large gold resource at Ladolam (>1,300 metric tons of gold), Lihir Island, resulted from the transition of an early-stage, low-grade porphyry gold system to a low-sulfidation epithermal gold event. This transition was probably triggered by rapid decompression during the partial slope failure of Luise stratovolcano and accompanied by the ingress of seawater. The original porphyry stage is indicated by remnant hydrothermal breccia clasts of strongly biotite–magnetite altered monzodiorite with disseminated pyrite ± chalcopyrite and poorly developed pyrite ± quartz stockwork veins. The breccias are overprinted by biotite–magnetite alteration and their matrix is strongly mineralized with disseminated auriferous pyrite. The breccias are cut by late-stage epithermal quartz–chalcedony–illite–adularia–pyrite veins and associated illite–adularia alteration that locally contain bonanza gold grades of up to 120 g/t. Isotope data suggest a magmatic source of sulfur in the gold-bearing fluids at Ladolam. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s00126-001-0230-y

Highlights of the international conference on catalytic gold, Cape Town, South Africa, 2–5 April 2001

The recent discoveries in a number of different laboratories that gold can be prepared in catalytically-active forms, and that these catalysts have special and attractive properties with commercial potential (1 – 5) were highlighted during this three day conference. This meeting brought together for the first time the world’s leading researchers in this field, and industrialists were able to assess the usefulness of the results obtained to date. Eighty-five delegates from fifteen different countries attended this conference, which was sponsored by both mining and industrial companies, eg World Gold Council, Anglogold, Mintek, and Engelhard-CLAL. There were representatives from six commercial applications companies and others were represented indirectly. There was the feeling of excitement often associated with the discovery of new science, particularly when there is also promise of new applications which will benefit society. The opening address was given by the South African Minister of Arts, Culture, Science and Technology, Dr S Ngubane. He said that it was highly appropriate that a conference on gold should take place in Southern Africa, source to date of at least 47,000 tons, or almost exactly one third of all the world’s gold, and it has been estimated that another 36,000 tons of gold remain, although some of it is not recoverable at present gold prices. Gold has been mined and used by the inhabitants of Southern Africa for at least 2,000 years: a beautiful gold rhinoceros is one of the many interesting artefacts recovered from the ancient city of Mapungubwe, in the far north of South Africa. There is enough gold in the world to support many future industrial applications and this is therefore good news for South Africa because gold and the gold mining industry contributes in a significant way to its economy. Consequently the South African government is pleased to note that the interest in using gold as a catalyst is growing. In my chairman’s introduction for the first session I commented on how my work as Technical Editor for Gold Bulletin has given me a good feel for uses of gold, which are not really very many: not as wide a spread as for the platinum group metals. One of the reasons for this is comparative lack of investigation: we are taught, from our earliest school chemistry lessons of the incorruptibility and lack of corrosivity of gold. Fortunately there were people present in the Cape Town audience who had disregarded this generalization and have found that catalysis by gold has special characteristics both when used homogeneously in solution and when used heterogeneously in the gas or liquid phase. I had learnt about new gold chemistry and new gold catalysis over the past five years or so, largely from my editor’s chair, and one of the exciting prospects for this conference was the opportunity of meeting many of these pioneer practitioners! The conference was divided into four sessions, ie ‘Catalytic Gold in the Synthesis of Fine Chemicals’, ‘Physical Characterization of Small Gold Particles’, ‘Catalytic Gold in Industrial Processes’ and ‘Catalytic Gold in Environmental Control’. There were five keynote lectures, and an evening workshop where lively discussion took place. The conference activities are summarized below:

Sulfur and lead isotope geochemistry of hypogene mineralization at the Barite Hill Gold Deposit, Carolina Slate Belt, southeastern United States: a window into and through regional metamorphism

The Barite Hill gold deposit, at the southwestern end of the Carolina slate belt in the southeastern United States, is one of four gold deposits in the region that have a combined yield of 110 metric tons of gold over the past 10 years. At Barite Hill, production has dominantly come from oxidized ores. Sulfur isotope data from hypogene portions of the Barite Hill gold deposit vary systematically with pyrite–barite associations and provide insights into both the pre-metamorphic Late Proterozoic hydrothermal and the Paleozoic regional metamorphic histories of the deposit. The δ34S values of massive barite cluster tightly between 25.0 and 28.0‰, which closely match the published values for Late Proterozoic seawater and thus support a seafloor hydrothermal origin. The δ34S values of massive sulfide range from 1.0 to 5.3‰ and fall within the range of values observed for modern and ancient seafloor hydrothermal sulfide deposits. In contrast, δ34S values for finer-grained, intergrown pyrite (5.1–6.8‰) and barite (21.0–23.9‰) are higher and lower than their massive counterparts, respectively. Calculated sulfur isotope temperatures for the latter barite–pyrite pairs (Δ=15.9–17.1‰) range from 332–355 °C and probably reflect post-depositional equilibration at greenschist-facies regional metamorphic conditions. Thus, pyrite and barite occurring separately from one another provide pre-metamorphic information about the hydrothermal origin of the deposit, whereas pyrite and barite occurring together equilibrated to record the metamorphic conditions. Preliminary fluid inclusion data from sphalerite are consistent with a modified seawater source for the mineralizing fluids, but data from quartz and barite may reflect later metamorphic and (or) more recent meteoric water input. Lead isotope values from pyrites range for 206Pb/204Pb from 18.005–18.294, for 207Pb/204Pb from 15.567–15.645, and for 208Pb/204Pb from 37.555–38.015. The data indicate derivation of the ore leads from the country rocks, which themselves show evidence for contributions from relatively unradiogenic, mantle-like lead, and more evolved or crustal lead. Geological relationships, and stable and radiogenic isotopic data, suggest that the Barite Hill gold deposit formed on the Late Proterozoic seafloor through exhalative hydrothermal processes similar to those that were responsible for the massive sulfide deposits of the Kuroko district, Japan. On the basis of similarities with other gold-rich massive sulfide deposits and modern seafloor hydrothermal systems, the gold at Barite Hill was probably introduced as an integral part of the formation of the massive sulfide deposit.

Tycho and the ton of gold

Tycho and the ton of gold

Source of Pb in orogenic lode-gold mineralisation: Pb isotope constraints from deep crustal rocks from the southwestern Archaean Yilgarn Craton, Australia

Southern Cross was one of the earliest gold mining centres in Western Australia. Over 142 tonnes of gold have been produced from the district, and, on a gold per hectare basis, the Southern Cross greenstone belt in the southwestern Yilgarn Craton is the most productive of Western Australia's Archaean greenstone belts. The SW Yilgarn Craton is characterised by high-grade (amphibolite- to granulite-facies) metamorphism, extensive granitoid magmatism and older greenstone volcanism ages, compared to the well-known greenschist-facies metamorphism and younger (2.7 Ga) eruption ages which dominate in the Eastern Goldfields Province. The Pb-isotope compositions of deep-seated granitoids in the SW Archaean Yilgarn Craton, which were emplaced coeval with a craton-wide major orogenic lode-gold mineralization event at about 2.64–2.63 Ga, have been determined for 96 whole-rock and 24 K-feldspar samples. The Pb isotope data of the granitoids are consistent with a crustal origin for their genesis, probably by reworking (partial melting) of older continental crust. The Pb isotope composition of greenstones, which are the main host rocks for gold mineralisation, and pyrites from the komatiite-hosted syngenetic Ni deposits in the amphibolite-facies Forrestania greenstone belt, have also been determined, with initial Pb-isotope ratios higher than that for the Eastern Goldfields Province. The Pb isotopic character of the orogenic lode-gold deposits in the region is intermediate between coeval granitoid and greenstone Pb, indicating that the ore fluids contained metals from both reservoirs. The Pb in the ore fluid of the most deeply formed deposit, Griffin's Find, overlaps the isotopic composition of coeval granitoids, indicating the deep-seated granitoid magmatism was the primary source for Pb in the ore fluids.