Fluid Inclusions, Stable Isotopes and Geochemistry of Porphyry Copper and Epithermal Vein Deposits of the Hauraki Gold - Silver Province, New Zealand

<p>Tertiary epithermal Au-Ag-Pb-Zn-Cu vein, and porphyry copper deposits occur in the Hauraki Province. The epithermal deposits were extensively mined for gold and silver in the late 1800's, and early 1900's and produced approximately 300 million grams (10 million ounces) of gold and 1,000 million grams (30 million ounces) of silver. They occur in Jurassic greywacke suite rocks, lower Miocene-Pliocene andesites and dacites, and upper Miocene-Pleistocene rhyolites although the deposits in the and esites and dacites produced most of the gold and silver mined. Base metal assemblages of the epithermal deposits are dominated by pyrite, sphalerite, galena and chalcopyrite, whereas acanthite and native gold (electrum) are the most common precious metal minerals. Tellurides (e.g. hessite) and seleniferous - selenide minerals are locally important. Gangue minerals are mainly quartz and calcite. Near neutral or slightly alkaline fluid pH is indicated for the epithermal fluids by the occurrence of sericite and/or adularia in wall rock alteration mineral assemblages. Acidic fluids, forming kaolinite, are characteristic of late stages or near surface environments. Fluid inclusion filling temperatures, and sulphur isotope temperatures from sphalerite-galena pairs, indicate that base metal deposition occurred mainly between 320 and. 280 degrees C, precious metal assemblages predominantly in the range of 280 - 200 degrees C and late stage barite, in some deposits, generally below 200 degrees C. There is fluid inclusion evidence for boiling during mineralisation in some deposits. Apparent salinities of the epithermal fluids, determined from fluid inclusion freezing temperatures, range from 0 - 6.1 eq. wt. % NaCl. No consistent difference in average apparent salinity was recognised between the different types of epithermal deposits, although the highest recorded values were from the base metal deposits. The absence of liquid CO2 in fluid inclusions limits the maximum possible concentration of CO2 to approximately 3 mole %. Extraction and measurement of CO2, from some samples indicates an average concentration of approximately 1 mole %. Corrections for dissolved CO2 required to transform apparent salinities to true salinities indicate that CO2 is the major solute in low salinity inclusions and that its concentration varied widely during mineral deposition in most deposits. Thermodynamic models of the geochemical environments of mineral deposition indicate that the large gold-silver deposits were formed by solutions in which sulphur occurred predominantly in reduced form, whereas many other deposits formed from solutions with approximately equal concentrations of oxidised and reduced aqueous sulphur species. Mineral deposition resulted from several different processes including: changes in fluid pH accompanying reactions with the wall rocks, mixing with other types of fluids, boiling, and variations in the concentration of CO2 in solution. These various processes acted separately in different parts of the hydrothermal system and general deposited characteristic mineral assemblages. Deuterium/hydrogen ratios of water extracted from fluid inclusions indicate that most hydrothermal fluids were originally meteoric water. Sulphur isotope ratios of sulphide and sulphate minerals, in association with the thermodynamic relations of the mineral assemblages, indicate that the sulphur was derived from at least two different sources; sedimentary sulphate and magmatic SO2, the relative importance of each varying from one deposit to another. Two types of hydrothermal systems are postulated for the formation of the epithermal deposits. During andesitic volcanism in the Miocene-early Pliocene, hydrothermal fluid convective cells were generated by heat from near surface small intrusive bodies of magma, whereas during rhyolitic volcanism in the late Miocene-Pleistocene the heat sources were larger plutons at greater depth. Porphyry copper deposits are associated with quartz diorite stocks intruded into Jurassic greywacke suite rocks and Miocene andesites. They are "diorite" model hypabyssal and volcanic types. The major minerals are quartz, pyrite, chalcopyrite and sphalerite. Additional minerals differ between the different deposits and define two contrasting geochemical environments of deposition, one characterised by low fS2, fO2 and Sigma S, indicated by the presence of pyrrhotite, and the other of moderate to high fS2, fO2 and Sigma S, indicated by the occurrence of bornite, magnetite or hematite. Associated hydrothermal alteration is generally propylitic although limited phyllic and "potassic" (defined by secondary biotite) types also occur in some deposits. Fluid inclusion and sulphur isotope studies of the Miners Head. porphyry copper deposit suggest that copper mineralisation occurred at a temperature of approximately 425 degrees C from fluids with apparent salinities up to.15.5 eq. wt. % NaCl and containing sulphur of magmatic origin, predominantly as H2S.</p>

Fluid Inclusions, Stable Isotopes and Geochemistry of Porphyry Copper and Epithermal Vein Deposits of the Hauraki Gold - Silver Province, New Zealand

<p>Tertiary epithermal Au-Ag-Pb-Zn-Cu vein, and porphyry copper deposits occur in the Hauraki Province. The epithermal deposits were extensively mined for gold and silver in the late 1800's, and early 1900's and produced approximately 300 million grams (10 million ounces) of gold and 1,000 million grams (30 million ounces) of silver. They occur in Jurassic greywacke suite rocks, lower Miocene-Pliocene andesites and dacites, and upper Miocene-Pleistocene rhyolites although the deposits in the and esites and dacites produced most of the gold and silver mined. Base metal assemblages of the epithermal deposits are dominated by pyrite, sphalerite, galena and chalcopyrite, whereas acanthite and native gold (electrum) are the most common precious metal minerals. Tellurides (e.g. hessite) and seleniferous - selenide minerals are locally important. Gangue minerals are mainly quartz and calcite. Near neutral or slightly alkaline fluid pH is indicated for the epithermal fluids by the occurrence of sericite and/or adularia in wall rock alteration mineral assemblages. Acidic fluids, forming kaolinite, are characteristic of late stages or near surface environments. Fluid inclusion filling temperatures, and sulphur isotope temperatures from sphalerite-galena pairs, indicate that base metal deposition occurred mainly between 320 and. 280 degrees C, precious metal assemblages predominantly in the range of 280 - 200 degrees C and late stage barite, in some deposits, generally below 200 degrees C. There is fluid inclusion evidence for boiling during mineralisation in some deposits. Apparent salinities of the epithermal fluids, determined from fluid inclusion freezing temperatures, range from 0 - 6.1 eq. wt. % NaCl. No consistent difference in average apparent salinity was recognised between the different types of epithermal deposits, although the highest recorded values were from the base metal deposits. The absence of liquid CO2 in fluid inclusions limits the maximum possible concentration of CO2 to approximately 3 mole %. Extraction and measurement of CO2, from some samples indicates an average concentration of approximately 1 mole %. Corrections for dissolved CO2 required to transform apparent salinities to true salinities indicate that CO2 is the major solute in low salinity inclusions and that its concentration varied widely during mineral deposition in most deposits. Thermodynamic models of the geochemical environments of mineral deposition indicate that the large gold-silver deposits were formed by solutions in which sulphur occurred predominantly in reduced form, whereas many other deposits formed from solutions with approximately equal concentrations of oxidised and reduced aqueous sulphur species. Mineral deposition resulted from several different processes including: changes in fluid pH accompanying reactions with the wall rocks, mixing with other types of fluids, boiling, and variations in the concentration of CO2 in solution. These various processes acted separately in different parts of the hydrothermal system and general deposited characteristic mineral assemblages. Deuterium/hydrogen ratios of water extracted from fluid inclusions indicate that most hydrothermal fluids were originally meteoric water. Sulphur isotope ratios of sulphide and sulphate minerals, in association with the thermodynamic relations of the mineral assemblages, indicate that the sulphur was derived from at least two different sources; sedimentary sulphate and magmatic SO2, the relative importance of each varying from one deposit to another. Two types of hydrothermal systems are postulated for the formation of the epithermal deposits. During andesitic volcanism in the Miocene-early Pliocene, hydrothermal fluid convective cells were generated by heat from near surface small intrusive bodies of magma, whereas during rhyolitic volcanism in the late Miocene-Pleistocene the heat sources were larger plutons at greater depth. Porphyry copper deposits are associated with quartz diorite stocks intruded into Jurassic greywacke suite rocks and Miocene andesites. They are "diorite" model hypabyssal and volcanic types. The major minerals are quartz, pyrite, chalcopyrite and sphalerite. Additional minerals differ between the different deposits and define two contrasting geochemical environments of deposition, one characterised by low fS2, fO2 and Sigma S, indicated by the presence of pyrrhotite, and the other of moderate to high fS2, fO2 and Sigma S, indicated by the occurrence of bornite, magnetite or hematite. Associated hydrothermal alteration is generally propylitic although limited phyllic and "potassic" (defined by secondary biotite) types also occur in some deposits. Fluid inclusion and sulphur isotope studies of the Miners Head. porphyry copper deposit suggest that copper mineralisation occurred at a temperature of approximately 425 degrees C from fluids with apparent salinities up to.15.5 eq. wt. % NaCl and containing sulphur of magmatic origin, predominantly as H2S.</p>

Preliminary Assessment of the Geological and Mining Heritage of the Golden Quadrilateral (Metaliferi Mountains, Romania) as a Potential Geotourism Destination

The Metaliferi Mountains (Western Romania) are known worldwide as the richest gold region in Romania and hosts for numerous porphyry and epithermal deposits. In these mountains, mining for gold dates back to Roman and even pre-Roman times. The Golden Quadrilateral constitutes a remarkable example of an area having a significant geological and mining heritage. The main purposes of this work are to emphasize this heritage, to present, for the first time, an assessment of the geological and mining heritage of the Golden Quadrilateral as a possible geotourism destination, and to point out the important role that geotourism could have in the sustainable development of local communities. To achieve our goals, the features of thirteen sites are presented, and two geotourism itineraries are proposed. A quantitative assessment of the geosites’ capacity to support scientific, educational, and geotourism/recreational uses indicates that the Golden Quadrilateral presents a high potential not only for scientific studies but, also, for enhancement of the public understanding of science; geotourism could be part of the development strategy of rural areas. The two museums (Gold Museum and Gold Mining Museum) can have an important contribution both to the geo-education of visitors and in promoting the sustainable development of the region.

Application of the Mineralogy and Mineral Chemistry of Carbonates as a Genetic Tool in the Hydrothermal Environment

The mineralogy and mineral chemistry of carbonates from various hydrothermal deposits, including volcanic-hosted Au-Cu epithermal, “Chilean Manto-type” Cu(-Ag), stratabound Mn, and Ag-Ba vein deposits from Spain and Chile, were investigated. Dolomite-ankerite (±siderite) was found in variable amounts within the epithermal deposits and associated hydrothermal alteration, whereas calcite was found either within barren veins or disseminated within the regional alteration. Calcite is the major gangue phase within the stratabound deposits, which tend to lack dolomite/ankerite and siderite. Carbonates precipitated from hydrothermal ore fluids are typically Mn-rich, up to 3.55 at. % in siderite, 2.27 at. % in dolomite/ankerite, and 1.92 at. % in calcite. In contrast, calcite related to very low-grade metamorphism or regional low-temperature alteration is Mn-poor but sometimes Mg-rich, possibly related to a higher temperature of formation. Chemical zonation was observed in the hydrothermal carbonates, although no unique pattern and chemical evolution was observed. This study suggests that the chemical composition of carbonates, especially the Mn content, could be a useful vector within ore-forming hydrothermal systems, and therefore constitutes a possible tool in geochemical exploration. Furthermore, Mn-poor calcites detected in some deposits are suggested to be linked with a later episode, maybe suggesting a predominance of meteoric waters, being not related to the main ore stage formation, thus avoiding misunderstanding of further isotopic studies.

Sphalerite Composition in Low- and Intermediate-Sulfidation Epithermal Ore Bodies from the Roșia Montană Au-Ag Ore Deposit, Apuseni Mountains, Romania

We evaluated the significance of the iron and manganese content in sphalerite as a tool for distinguishing between low-sulfidation and intermediate-sulfidation epithermal deposits on the basis of new and previously published electron probe microanalyses data on the Roșia Montană epithermal ore deposit and available microchemical data from the Neogene epithermal ore deposits located in the Apuseni Mountains and Baia Mare region, Romania. Two compositional trends of the Fe vs. Mn content in sphalerite were delineated, a Fe-dominant and a Mn-dominant, which are poor in Mn and Fe, respectively. The overlapping compositional range of Fe and Mn in sphalerite in low-sulfidation and intermediate-sulfidation ores suggests that these microchemical parameters are not a reliable tool for distinguishing these epithermal mineralization styles.

The ROBOMINERS project: a promising tool for the re-evaluation of “non-economical” deposits. Aiming at the development of a joined European database of potentially suitable ore deposits for the utilization of the Robominers technology.

&lt;p&gt;The ROBOMINERS (Resilient Bio-inspired Modular Robotic Miner) project aims at developing new methods and technologies (prototype automation and robotics technology) to locate and exploit underground mineral deposits and is funded under the European Union&amp;#8217;s Research and Innovation programme Horizon 2020. The project targets mineral deposits that are generally considered &amp;#8220;non-economical&amp;#8221; either because they are not accessible anymore for conventional mining techniques, or they have been previously explored but exploitation was considered uneconomic due to the small size of the deposits or the difficulty to access them (abandoned, small, ultra-depth deposits).&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;The European Federation of Geologists (EFG) is part of the Robominers consortium and its role includes the collection of publicly available data at a national level on mineral deposits which are potential targets on the developed mining technology. The Association of Greek Geologists (AGG) is participating as an EFG Linked Third Party in the project aiming, among others, at the creation of a European database of potentially suitable ore deposits for the utilization of the Robominers technology.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;The creation of an ore deposits&amp;#8217; European database is a crucial procedure for the best possible design of exploration and exploitation applying the Robominers innovative approach. The AGG has contributed in the building of a database at a national level (for Greece), of the major and most important mineral deposits, according to the project requirements. A number of ore deposits in which Robominers advanced technology may provide a unique solution to mineral extraction, include porphyry and epithermal deposits and especially vein-like types, but volcanogenic massive sulphide (VMS-type) and lense-like or layered orthomagmatic deposits can also be of high importance. From the above mentioned ore deposits the most abundant in Greece are epithermal deposits, deposits in hydrothermal veins, porphyry copper, as well as chromites in ophiolite complexes. Regarding the spatial distribution vein-type or metasomatic deposits are located mostly in Northern Greece (Western Macedonia and Thrace regions) while significant variable-mineralization deposits are related with the Attico-Cycladic belt volcanism (mainly Lavrion, Evia, and islands in the Aegean Sea). Finally, PGE bearing chromite deposits and bauxite deposits, located mainly in Central Greece, may also be significant for the project.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;The establishment of a joined European Robominers database is of great significance for the progress of the project since it will provide essential information on key outputs such as the deposit type and commodities, the host rock, and the spatial distribution of the project&amp;#8217;s targeted ore deposits and will provide valuable knowledge regarding the future planning of the exploration and exploitation from the developed Robominers innovative technology approach.&lt;/p&gt;&lt;p&gt;Dr Eleni Koutsopoulou&lt;/p&gt;&lt;p&gt;Coordinator of the project&lt;/p&gt;&lt;p&gt;On Behalf of the:&lt;/p&gt;&lt;p&gt;Association of Greek Geologists&lt;/p&gt;&lt;p&gt;Didotou 26,10680, Athens, Greece&lt;/p&gt;&lt;p&gt;VAT ID: EL-999600130&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

Metallogeny of the Zahedan-Nehbandan magmatic belt and implications to porphyry Cu exploration in southeastern Iran

&lt;p&gt;The Late Cretaceous to Eocene Sistan suture zone in southeastern Iran separates the Lut continental block in the west from the Afghan continental block in the east. A major belt of Oligocene to Miocene igneous rocks occurs between the cities of Zahedan and Nehbandan, stretching for ~200 km from south to north parallel to the border with Pakistan and Afghanistan. Known porphyry Cu mineralization is associated with the intrusions and intrusive complexes at Kuh-e Janja (16.5+2.0 Ma), Kuh-e Seyasteragi (19.2+ 1.4 Ma), Kuh-e Assagie (27.5+2.0 Ma), and Kuh-e Lar (32.8+3.0 Ma).&lt;/p&gt;&lt;p&gt;Small intrusions and intrusive complexes in the Zahedan-Nehbandan magmatic belt are mostly intermediate to felsic in composition and have calc-alkaline or shoshonitic affinities. Associated volcanic and volcaniclastic rocks are common. The igneous rocks are hosted by deformed late Cretaceous to Eocene flysch sequences that formed in the Sefidabeh forearc basin developed during the subduction and closure of the Sistan ocean. The geochemical composition of the intrusive rocks and their ages suggest that igneous activity and related mineralization in the Zahedan-Nehbandan magmatic belt may have formed as a result of post-collisional processes. The locations of the intrusive centers in the Kuh-e Assagie and Kuh-e Lar may be controlled by strike-slip faults, which are major post-collisional structures.&lt;/p&gt;&lt;p&gt;The recent discovery of the Janja porphyry Cu-Au-Mo deposit below Quaternary alluvial terraces highlights the exploration potential of the Zahedan-Nehbandan magmatic belt. In addition to post-collisional porphyry deposits, other deposit types such as skarns, polymetallic veins, or epithermal deposits may be hidden below the regionally extensive Quaternary cover.&lt;/p&gt;