For economic geologists, mineral exploration has a specific objective: the discovery of mineral concentrations that can be recovered economically to provide resources essential for society. This was achieved consistently until the first decade of the current century, but exploration since then has been wealth destructive. This outcome is a major issue for the mining industry unless reversed. We believe the technologies presently used to discover ore deposits will be as useful in making future discoveries as they were previously. However, we argue that a new approach is required in how exploration is conducted and in how these and emerging technologies are applied. The required changes in approach include improved business models for conducting exploration and acceptance that fewer deposits are likely to be discovered near the surface. We argue that discovery of deeper deposits will be facilitated if exploration teams (1) seek to identify subtle evidence of mineralized rock recognizable within 500 m of the surface, (2) conduct follow-up investigations with a clear understanding of the volumetric dimensions of the discovery target, and (3) drill boldly as a critical exploration tool. We propose that improving the way geoscientists think when exploring—being more predictive—is the immediate key to increasing the number of discoveries.

Mineral exploration since 2005 in a previously underexplored region of southwestern Mongolia resulted in the definition of the Zuun Mod porphyry Mo-Cu deposit, followed by discovery of the Altan Nar and Bayan Khundii epithermal gold deposits along with several prospects and advanced exploration projects. These discoveries form the core of the emerging Khundii ("Valley") metallogenic province, -50 x 100 km in size, located within a single island-arc terrane of Middle Carboniferous to early Permian age and predominantly within an individual mapped subterrane. The province is situated -700 km west-northwest of the late Devonian Oyu Tolgoi porphyry Cu-Au deposit in a belt of mid-Paleozoic island arcs that are part of the Central Asian orogenic belt, host to world-class porphyry Cu-Au and epithermal gold deposits that stretch from southern Mongolia to the west, into China, Kazakhstan, and beyond. The Zuun Mod porphyry Mo-Cu deposit (297 +/- 4.8 Ma) is hosted by a granodiorite intrusion cut by B-type quartz-molybdenite-chalcopyrite veins with K-feldspar alteration selvages plus disseminated biotite and magnetite. After definition of this deposit, a regional exploration program was initiated in 2009 over 110,000 km2, based on the underexplored nature of the region. Exploration included compilation of existing geologic, geochemical, and geophysical data and interpretation of satellite imagery followed by ground exploration that included stream, soil, and rock-chip sampling and geologic and alteration mapping. The Nomin Tal Cu-Au prospect was discovered in early 2011, and based on the indications from initial soil sampling, a 400- x 400-m soil survey was conducted over the southern part of the exploration license, which identified a Pb-, Zn-, and Au-in-soil anomaly over an area of -1.5 x -5.5 km. The first drill hole within the soil anomaly in late 2011 resulted in the discovery of the Altan Nar Au-polymetallic epithermal deposit with veins of coarsely crystalline quartz-adularia (309.7 +/- 0.5 Ma) and Ca-, Mg-, Mn-, and Fe-carbonate gangue that host the base metal sulfides. The Bayan Khundii gold deposit was discovered in 2015 as the result of prospecting, -16 km southeast of Altan Nar. Subsequent discovery of the Khar Mori gold project was announced in early 2021, -3 km north of Bayan Khundii along a structural trend, and later in 2021 drilling discovered wide zones of disseminated gold at Ulaan Southeast, -800 m west of Bayan Khundii. The epithermal quartz-adularia-gold veins (336.8 +/- 0.5 Ma) at Bayan Khundii have colloform bands with minor pyrite and are enveloped by proximal illite alteration. The epithermal veins and alteration overprint an earlier, unrelated alteration style of residual quartz and pyrophyllite +/- dickite +/- diaspore-kaolinite. Similarly, residual quartz and pyrophyllite-dickite at Khar Mori are overprinted by epithermal mineralization, including arsenopyrite. At the central Ulaan project, -3 km northwest of Bayan Khundii, intense quartz-white mica-pyrite alteration is widespread at surface, including tourmaline bodies and local copper anomalies, associated with nearby residual quartz and related aluminosilicate alteration. These alteration styles indicate erosion of a lithocap to its base, exposing K-feldspar and magnetite plus quartz-white mica-pyrite related to the top of a porphyry deposit, as yet only tested by a few scout drill holes. The undated porphyryrelated alteration was subsequently overprinted by the gold-bearing epithermal veins after significant erosion.

Advanced argillic minerals, as defined, include alunite and anhydrite, aluminosilicates (kaolinite, halloysite, dickite, pyrophyllite, andalusite, zunyite, and topaz), and diaspore. One or more of these minerals form in five distinctly different geologic environments of hydrolytic alteration, with pH 4-5 to <1, most at depths <500 m. (1) Where an intrusion-related hydrothermal system, typical of that associated with porphyry Cu +/- Au deposits, evolves to white-mica stability, continued ascent and cooling of the white-mica-stable liquid results in pyrophyllite (+/- diaspore) becoming stable near the base of the lithocap. (2) A well-understood hypogene environment of formation is vapor condensation near volcanic vents, where magmatic SO2 and HCl condense into local groundwater to produce H2SO4 and HCl-rich solutions with a pH of 1-1.5. Close to isochemical dissolution of the host rock occurs because of the high solubility of Al and Fe hydroxides at pH <2, except for the SiO2 component, which remains as a siliceous residue because of the relatively low solubility of SiO2. This residual quartz, commonly with a vuggy texture, is largely barren of metals because of the low metal content in high-temperature but low-pressure volcanic vapor. Rock dissolution causes the pH of the acidic solution to increase, such that alunite and kaolinite (or dickite or pyrophyllite at higher temperatures) become stable, forming a halo to the residual quartz. This initially barren residual quartz, which forms a lithocap horizon where permeable lithologic units are intersected by the feeder structure, may become mineralized if a subsequent white-mica- stable liquid ascends to this level and precipitates copper and gold. (3) Boiling of a hydrothermal liquid generates vapor with CO2 and H2S. Where the vapor condenses above the water table, atmospheric O-2 in the vadose (unsaturated) zone causes oxidation of H2S to sulfuric acid, forming a steam-heated acid-sulfate solution with pH of 2-3. In this environment, kaolinite and alunite form in horizons above the water table at <100 degrees C. Silica derived within the vadose zone will precipitate as amorphous silica at the water table, as the condensate follows the hydraulic gradient, causing opal replacement above and at the aquifer. (4) By contrast, where condensation of this vapor occurs below the water table, the CO2 in solution forms carbonic acid (H2CO3), leading to a pH of 4-5. This marginal carapace of condensate, with temperatures up to 150 degrees-170 degrees C, commonly acts as a diluent of the ascending parental NaCl liquid. This steam-heated liquid forms intermediate argillic alteration of clays, kaolinite, and Fe-Mn carbonates; this kaolinite, which can be present at depths of several hundreds of meters, can potentially be mistaken as having been caused by a steam-heated acid-sulfate or supergene overprint. (5) The final setting is supergene, caused by posthydrothermal weathering and oxidation of mainly pyrite, locally creating pH <1 liquid because of high concentrations of H2SO4 within the vadose zone and forming kaolinite, alunite, and Fe oxyhydroxides. This genetic framework of formation environments of advanced (and intermediate) argillic alteration provides the basis to interpret alteration mineralogy, in combination with alteration textures and morphology plus zonation, including the overprint of one alteration style on another. This framework can be used to help focus exploration for and assessment of hydrothermal ore deposits, including epithermal, porphyry, and volcani-chosted massive sulfide.

Ninety-eight underground diamond holes (-102 km) drilled by Far Southeast Gold Resources Inc. at the Far Southeast porphyry Cu-Au deposit, Philippines, from 2011 to mid-2013, provide a three-dimensional exposure of the deposit between 700-and -750-m elevation, with surface at-1,400-m elevation. Far Southeast contains an inferred resource of 891.7 million tonnes (Mt) averaging 0.7 g/t Au and 0.5 wt % Cu, equivalent to 19.8 Moz Au and 4.5 Mt Cu. This contribution reports the spatial and temporal distribution of alteration and mineralization at Far Southeast, notably a white-mica-chlorite-albite assemblage that formed after early secondary biotite and before late quartz-white-mica-pyrite alteration and that is associated with the highest copper and gold grades.Alteration assemblages were determined by drill core logging, short-wavelength infrared (SWIR) spectral analysis, petrographic examination, and a quantitative evaluation of materials by scanning electron microscopy (QEMSCAN) study. Alteration is limited around sparse veins or pervasive where vein density is high and the alteration halos coalesce. The alteration and mineralization zones with increasing depth are as follows: (1) the lithocap of quartz-alunite-dominated advanced argillic-silicic alteration that hosts part of the Lepanto high-sulfidation Cu-Au epithermal deposit (mostly above-700-m elevation), (2) an aluminosilicate-dominated zone with coexisting pyrophyllite-diaspore +/- kandite +/- alunite and white mica (-700-to-100-m elevation), (3) por-phyry-style assemblages characterized by stockwork veins (below-500-m elevation), (4) the 1 wt % Cu equiva-lent ore shell (-400-to -300-m elevation), and (5) an underlying subeconomic zone (about -300-to -750-m elevation, the base of drilling). The ore shells have a typical bell shape centered on a dioritic intrusive complex.The paragenetic sequence of the porphyry deposit includes stage 1 granular gray to white quartz-rich (+/- anhy-drite +/- magnetite +/- biotite) veins with biotite-magnetite alteration. These were cut by stage 2 lavender-colored euhedral quartz-rich (+/- anhydrite +/- sulfides) veins, with halos of greenish white-mica-chlorite-albite alteration. The white mica is largely illite, with an average 2,203-nm Al-OH wavelength position. The albite may reflect the mafic nature of the diorite magmatism. The quartz veins of this stage are associated with the bulk of copper deposited as chalcopyrite and bornite, as well as gold. Thin Cu sulfide (chalcopyrite, minor bornite) veins with minor quartz and/or anhydrite (paint veins), with or without a white-mica halo, also occur. These veins were fol-lowed by stage 3 anhydrite-rich pyrite-quartz veins with white-mica (avg 2,197 nm, illite)-pyrite alteration halos.Combined with previous studies, we conclude that this porphyry system, including the Far Southeast por-phyry and Lepanto high-sulfidation Cu-Au deposits, evolved over a period of 0.1-0.2 m.y. Three diorite por-phyry stocks were emplaced, and by-1.4 Ma biotite-magnetite-style alteration formed with quartz-anhydrite veins and deposition of 50.5% Cu and 50.5 g/t Au (stage 1); coupled with this alteration style, a barren lithocap of residual quartz with quartz-alunite halo plus kandite +/- pyrophyllite and/or diaspore formed at shallower depth (>700-m elevation). Subsequently, lavender quartz and anhydrite veins with bornite and chalcopyrite (high-grade stage, avg-1 wt % Cu and-1 g/t Au) and white-mica-chlorite-albite halos formed below-400-m elevation (stage 2). They were accompanied by local pyrite replacement, the formation of hydrothermal brec-cias and Cu sulfide (paint) veins. Stage 2 was followed at-1.3 Ma by the formation of igneous breccias largely along the margins of the high-grade zones and stage 3 pyrite-quartz-anhydrite +/- chalcopyrite veins with white -mica (mostly illitic) halos. At shallower depths in the transition to the base of the lithocap, cooling led to the formation of aluminosilicate minerals (mainly pyrophyllite +/- diaspore +/- dickite) with anhydrite plus high-sul-fidation-state sulfides and pyrite veinlets. Consistent with previous studies, it is likely that the lithocap-hosted enargite-Au mineralization formed during this later period.

Alteration mineralogy from shortwave infrared (SWIR) spectroscopy was compared with X-ray diffraction (XRD) analyses for samples from the Zhengguang intermediate sulfidation epithermal Au-Zn deposit, eastern Central Asian orogenic belt, northeast China. The SWIR and XRD analyses indicate that alteration minerals in the vein-adjacent halo mainly comprise quartz, illite, and locally pyrite (QIP) and chlorite, whereas samples from the pervasive propylitic alteration of host basaltic andesite lava contain epidote, chlorite, carbonate, montmorillonite, and locally illite. SWIR mineral identifications from automated mineral identification software may not always be accurate; thus, the results should be validated by the user. The wavelength position of the Al-OH (~2,200 nm; wAlOH) absorption feature can be used to approximate the composition of illite or white mica. However, caution is required when using the wAlOH value to assess paleotemperatures, as the composition of illite can be influenced by the composition of the host rocks or the hydrothermal fluid. In addition, values of the illite spectral maturity (ISM; ratio of the depth of the ~2,200 nm minima divided by the ~1,900 nm minima) can be affected by the presence of other hydrous minerals, quartz-sulfide veins, and absorption intensity (which can be a function of rock coloration). Despite these cautions, the spatial distribution and variation of the wAlOH and ISM values for illite suggest that the high paleotemperature hydrothermal upflow zones related to the Zhengguang Au-Zn deposit were located below ore zones I and IV, which are predicted to be proximal to the intrusive center of the system.

Surface samples of hypogene alunite that cement late breccia bodies from the El Salvador porphyry copper district of Chile were recently dated. One alunite sample over the principal Turquoise Gulch porphyry deposit has a 40Ar/ 39Ar total gas age of 40.64 +/- 1.04 Ma, overlapping the age of a late latite intrusion. Two other samples associated with quartz-alunite replacement of rhyolite, similar to 750 m southwest of the collapse zone over the block cave of the porphyry copper deposit, are distinctly younger, at 38.12 +/- 0.66 and 38.04 +/- 0.22 Ma (averages of duplicate analyses, with +/- 2 sigma errors). Previously reported U/Pb ages of zircons from 15 Eocene-age diorite, granodiorite, and granite porphyry intrusions have weighted mean ages that range from about 44 to 41 Ma, with peak magmatic flux interpreted at 44 to 43 Ma. Porphyry copper ores in the El Salvador district formed at about the same time as porphyry intrusions, with intrusive centers that migrated in a south-southwest direction, from the small deposits at Cerro Pelado (similar to 44.2 Ma), to Old Camp (similar to 43.6 Ma) and M Gulch-Copper Hill (similar to 43.5-43.1 Ma), to the main ore deposit at Turquoise Gulch (similar to 42 Ma). The granodiorite porphyry intrusions at Turquoise Gulch are associated with similar to 80% of the known copper ore of the district; they record waning stages of magmatism at 42.5 to 42.0 Ma, followed by weakly altered latite dikes at 41.6 Ma. Molybdenite in quartz veins returned Re-Os ages of 41.8 to 41.2 Ma. The two alunite samples from our study with coincident dates of similar to 38 Ma provide evidence for magmatichydrothermal activity younger than any recognized to date, consistent with the alteration overprint of quartzalunite on older muscovite after erosion. This younger activity must have been associated with a blind intrusion, likely located south of the Turquoise Gulch deposit, based on the distribution of alteration minerals, and offset from the zoning associated with the Turquoise Gulch center. Stable isotope values (delta S-34, delta O-18, delta D) of the similar to 38 Ma alunite indicate a high-temperature hypogene origin, consistent with formation in a lithocap environment that typically is located at shallow levels over and on the shoulders of porphyry copper deposits. Both observations-alteration overprint and markedly younger age of alunite-indicate the potential for porphyry copper mineralization south of Granite Gulch, as much as 1,000 m below the level of the coeval outcropping quartzalunite replacement, perhaps near similar to 2,000-m elevation; this is hundreds of meters deeper than the known copper ore of Turquoise Gulch. Surface samples of hypogene alunite that cement late breccia bodies from the El Salvador porphyry copper district of Chile were recently dated. One alunite sample over the principal Turquoise Gulch porphyry deposit has a 40Ar/ 39Ar total gas age of 40.64 +/- 1.04 Ma, overlapping the age of a late latite intrusion. Two other samples associated with quartz-alunite replacement of rhyolite, similar to 750 m southwest of the collapse zone over the block cave of the porphyry copper deposit, are distinctly younger, at 38.12 +/- 0.66 and 38.04 +/- 0.22 Ma (averages of duplicate analyses, with +/- 2 sigma errors). Previously reported U/Pb ages of zircons from 15 Eocene-age diorite, granodiorite, and granite porphyry intrusions have weighted mean ages that range from about 44 to 41 Ma, with peak magmatic flux interpreted at 44 to 43 Ma. Porphyry copper ores in the El Salvador district formed at about the same time as porphyry intrusions, with intrusive centers that migrated in a south-southwest direction, from the small deposits at Cerro Pelado (similar to 44.2 Ma), to Old Camp (similar to 43.6 Ma) and M Gulch-Copper Hill (similar to 43.5-43.1 Ma), to the main ore deposit at Turquoise Gulch (similar to 42 Ma). The granodiorite porphyry intrusions at Turquoise Gulch are associated with similar to 80% of the known copper ore of the district; they record waning stages of magmatism at 42.5 to 42.0 Ma, followed by weakly altered latite dikes at 41.6 Ma. Molybdenite in quartz veins returned Re-Os ages of 41.8 to 41.2 Ma. The two alunite samples from our study with coincident dates of similar to 38 Ma provide evidence for magmatichydrothermal activity younger than any recognized to date, consistent with the alteration overprint of quartzalunite on older muscovite after erosion. This younger activity must have been associated with a blind intrusion, likely located south of the Turquoise Gulch deposit, based on the distribution of alteration minerals, and offset from the zoning associated with the Turquoise Gulch center. Stable isotope values (delta S-34, delta O-18, delta D) of the similar to 38 Ma alunite indicate a high-temperature hypogene origin, consistent with formation in a lithocap environment that typically is located at shallow levels over and on the shoulders of porphyry copper deposits. Both observations-alteration overprint and markedly younger age of alunite-indicate the potential for porphyry copper mineralization south of Granite Gulch, as much as 1,000 m below the level of the coeval outcropping quartzalunite replacement, perhaps near similar to 2,000-m elevation; this is hundreds of meters deeper than the known copper ore of Turquoise Gulch. Surface samples of hypogene alunite that cement late breccia bodies from the El Salvador porphyry copper district of Chile were recently dated. One alunite sample over the principal Turquoise Gulch porphyry deposit has a 40Ar/ 39Ar total gas age of 40.64 +/- 1.04 Ma, overlapping the age of a late latite intrusion. Two other samples associated with quartz-alunite replacement of rhyolite, similar to 750 m southwest of the collapse zone over the block cave of the porphyry copper deposit, are distinctly younger, at 38.12 +/- 0.66 and 38.04 +/- 0.22 Ma (averages of duplicate analyses, with +/- 2 sigma errors). Previously reported U/Pb ages of zircons from 15 Eocene-age diorite, granodiorite, and granite porphyry intrusions have weighted mean ages that range from about 44 to 41 Ma, with peak magmatic flux interpreted at 44 to 43 Ma. Porphyry copper ores in the El Salvador district formed at about the same time as porphyry intrusions, with intrusive centers that migrated in a south-southwest direction, from the small deposits at Cerro Pelado (similar to 44.2 Ma), to Old Camp (similar to 43.6 Ma) and M Gulch-Copper Hill (similar to 43.5-43.1 Ma), to the main ore deposit at Turquoise Gulch (similar to 42 Ma). The granodiorite porphyry intrusions at Turquoise Gulch are associated with similar to 80% of the known copper ore of the district; they record waning stages of magmatism at 42.5 to 42.0 Ma, followed by weakly altered latite dikes at 41.6 Ma. Molybdenite in quartz veins returned Re-Os ages of 41.8 to 41.2 Ma. The two alunite samples from our study with coincident dates of similar to 38 Ma provide evidence for magmatichydrothermal activity younger than any recognized to date, consistent with the alteration overprint of quartzalunite on older muscovite after erosion. This younger activity must have been associated with a blind intrusion, likely located south of the Turquoise Gulch deposit, based on the distribution of alteration minerals, and offset from the zoning associated with the Turquoise Gulch center. Stable isotope values (delta S-34, delta O-18, delta D) of the similar to 38 Ma alunite indicate a high-temperature hypogene origin, consistent with formation in a lithocap environment that typically is located at shallow levels over and on the shoulders of porphyry copper deposits. Both observations-alteration overprint and markedly younger age of alunite-indicate the potential for porphyry copper mineralization south of Granite Gulch, as much as 1,000 m below the level of the coeval outcropping quartzalunite replacement, perhaps near similar to 2,000-m elevation; this is hundreds of meters deeper than the known copper ore of Turquoise Gulch.

Editor’s note: The Geology and Mining series, edited by Dan Wood and Jeffrey Hedenquist, is designed to introduce early-career professionals and students to a variety of topics in mineral exploration, development, and mining, in order to provide insight into the many ways in which geoscientists contribute to the mineral industry. Abstract For economic geologists, mineral exploration has a specific objective: the discovery of mineral concentrations that can be recovered economically to provide resources essential for society. This was achieved consistently until the first decade of the current century, but exploration since then has been wealth destructive. This outcome is a major issue for the mining industry unless reversed. We believe the technologies presently used to discover ore deposits will be as useful in making future discoveries as they were previously. However, we argue that a new approach is required in how exploration is conducted and in how these and emerging technologies are applied. The required changes in approach include improved business models for conducting exploration and acceptance that fewer deposits are likely to be discovered near the surface. We argue that discovery of deeper deposits will be facilitated if exploration teams (1) seek to identify subtle evidence of mineralized rock recognizable within 500 m of the surface, (2) conduct follow-up investigations with a clear understanding of the volumetric dimensions of the discovery target, and (3) drill boldly as a critical exploration tool. We propose that improving the way geoscientists think when exploring—being more predictive—is the immediate key to increasing the number of discoveries.

Book Review| May 01, 2019 Atlas of Siliceous Hot Spring Deposits (Sinter) and other Silicified Surface Manifestations in Epithermal Environments (A.R. Hamilton, K.A. Campbell, and D.M. Guido) Jeffrey W. Hedenquist Jeffrey W. Hedenquist Ottawa, Ontario March 25, 2019 Search for other works by this author on: GSW Google Scholar Economic Geology (2019) 114 (3): 591–592. https://doi.org/10.5382/econgeo.114.3.br01 Article history first online: 09 May 2019 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Jeffrey W. Hedenquist; Atlas of Siliceous Hot Spring Deposits (Sinter) and other Silicified Surface Manifestations in Epithermal Environments (A.R. Hamilton, K.A. Campbell, and D.M. Guido). Economic Geology 2019;; 114 (3): 591–592. doi: https://doi.org/10.5382/econgeo.114.3.br01 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEconomic Geology Search Advanced Search Atlas of Siliceous Hot Spring Deposits (Sinter) and other Silicified Surface Manifestations in Epithermal Environments. A. R. Hamilton, K. A. Campbell, and D. M. Guido. New Zealand Geological and Nuclear Science Report 2019/06, February 2019. doi:10.21420/BQDR-XQ16. Open Access: https://drive.google.com/file/d/1m5QPfrzi2veKVznh1YS97wtbK6VP-VH0/view. This 62-page open-file report of the New Zealand Institute of Geological and Nuclear Sciences is a useful atlas of surface features and textures from active geothermal systems, mainly from the Taupo volcanic zone, New Zealand, and Yellowstone National Park, particularly deposits of amorphous silica around discharging hot springs. The report compares observations of these textures with examples of paleosurface features... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Volcanic complexes in Japan such as Kusatsu Shirane, Honshu, and Kuju-Hatchobaru and Kirishima, Kyushu, host active magmatic-hydrothermal systems that are several kilometers in diameter and typically asymmetric to the intrusive center. Their heat flow is driven by multiple intrusions at <5-10km depth over a period on the order of similar to 10(5)years. These hydrothermal systems consist of advecting fluids of magmatic origin (either vapor with acidic components condensed into meteoric water, or a subsequent liquid of varying reactivity) that interact with convecting meteoric water. The amount of the magmatic component depends on location relative to the intrusive center, local controls on permeability, and the temporal evolution of the intrusions. The proportion of meteoric water diluent typically increases from proximal to distal locations (over several kilometer distance), and with time after intrusion (> several thousands of years). Some of the neutral pH solutions in these large hydrothermal systems, up to similar to 5km from volcanic vents, support geothermal energy developments, with strong structural control on fluid flow. Near active volcanic vents, the magmatic vapor component of hydrothermal systems can form acidic condensates (pH similar to 1.5) that are responsible for strong alteration of the host rock. The resulting residual quartz and advanced argillic minerals are typical of shallow-formed lithocap alteration that is associated with deeper porphyry copper deposits in similar arc-hosted volcanic settings. Around the world, this near-surface lithocap alteration, influenced by structures as well as lithology, may be barren in metals, even where associated with mineralized porphyry intrusions at depth. Such intrusion-proximal alteration is widespread in both active and extinct settings in Japan. In addition, distal geothermal hot springs typically have a magmatic water component, albeit minor, with a pH that varies from similar to 3 to near-neutral; deep alteration intersected in drill holes is characterized by alunite-dickite-pyrophyllite or chlorite-wairakite, respectively. These alteration assemblages are typical of their extinct equivalents, intermediate sulfidation epithermal veins, with mineralogical complexities caused by temporal evolution as well as spatial variation (e.g. along different structures). Such active and extinct magmatic-hydrothermal systems signify the presence of shallow degassing or degassed intrusions, respectively. Where similar intrusions in volcanic arcs around the world are eroded to similar to 1 to 2km depth, the tops of porphyry copper deposits are commonly exposed, marked by a transition of white mica upward to pyrophyllite-dominant alteration. Active magmatic-hydrothermal systems on the flanks of arc volcanoes in Japan are dynamic - both cycling as well as evolving - and share characteristics with extinct systems that host epithermal and porphyry ore deposits.

Research Article| September 01, 2018 Geology of Mineral Resources (Michel Jébrak and Éric Marcoux) Jeffrey W. Hedenquist Jeffrey W. Hedenquist University of Ottawa Ottawa, Canada July 24, 2018 Search for other works by this author on: GSW Google Scholar Author and Article Information Jeffrey W. Hedenquist University of Ottawa Ottawa, Canada July 24, 2018 Publisher: Society of Economic Geologists First Online: 23 Oct 2018 Online Issn: 1554-0774 Print Issn: 0361-0128 © 2018 Economic GeologyEconomic Geology Economic Geology (2018) 113 (6): 1447. https://doi.org/10.5382/econgeo.113.6.br01 Article history First Online: 23 Oct 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Jeffrey W. Hedenquist; Geology of Mineral Resources (Michel Jébrak and Éric Marcoux). Economic Geology 2018;; 113 (6): 1447. doi: https://doi.org/10.5382/econgeo.113.6.br01 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEconomic Geology Search Advanced Search Geology of Mineral Resources. Michel Jébrak and Éric Marcoux. Geological Association of Canada, 2015. Pp. 668. ISBN: 978-1-897-09573-7. Price Hardback, CAD$81.81; Members CAD$45.00. (https://www.gac.ca/publications.php) Preparation of a textbook on the subject of economic geology is a daunting task due to the broad range of topics that must be covered in a consistent and balanced fashion, with an adequate understanding of each topic to provide a clear explanation to nonspecialists. Michel Jébrak and Éric Mar-coux tackled this task and have done a commendable job. I know of no better volume to introduce senior undergraduate and graduate students to the... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The discovery of new resources is challenging both in well-understood geological environments and new settings (Section 3). Successful discovery does not, however, guarantee economic and socially acceptable exploitation. In this section, we review the range of mining and metallurgical processes

Metals and mineral products are essential for modern society. They are found in the products we use every day, from kitchen utensils to cell phones to refrigerators. They are the basis for construction of homes, offices and bridges, and manufacturing of cars, trains and aeroplanes, and they are

Our continuing global mineral needs must come from reserves and resources. Recall from Section 1 that the term “resources” refers to Earth’s entire inventory of the mineral of interest, whereas “reserves” refer to that part of the resources that have been identified and quantified and can

The general features of ore deposits in the epithermal environment are influenced by their tectonic, magmatic and geologic associations. Geologic variability means that there is a wide variation in features associated with individual districts, deposits, and prospects. In this presentation we review some of the first-order features relevant to exploration and assessment of epithermal deposit targets. Our recommendations combine knowledge from traditional and recent geologic and genetic models with personal lessons from exploration and published exploration case studies. These recommendations provide a framework for investigation and documentation of key features such as genetic models and deposit classification, depth of formation, alteration mineralogy and zoning, and ore and gangue assemblages and textures, among others. Use of this framework for the design and later interpretation of geochemical and geophysical surveys will assist greatly in the development and testing of epithermal precious- and base-metals exploration targets.

The term “ore deposit” has a specific meaning in the geological literature (Section 1), being a mass of rock that contains a useful element, compound or mineral with a grade (concentration) and total amount sufficiently high that the material can be mined economically. Copper, Au and Fe are the

Mineral exploration is the first stage of wealth creation from mining ([Fig. 3.1][1]; [Agricola, 1556][2] [[Box 4.2][3]]; [Porter, 1985][4]). ![Figure 3.1][5] Figure 3.1 Mining Value Chain (modified from [Camus, 2011][6]). Exploration and mining started in the Neolithic, preceding

Some scientists and journalists, and many members of the general public, have been led to believe that the world is rapidly running out of the metals on which our modern society is based. Advocates of the peak metal concept have predicted for many decades that increasing consumption will soon lead to exhaustion of mineral resources. Yet, despite ever-increasing production and consumption, supplies of minerals have continued to meet the needs of industry and society, and lifetimes of reserves remain similar to what they were 30-40 years ago.In this volume, we discuss the reasons for this apparent paradox using our broad experience and expertise on both academic and industrial sides of the minerals sector. Many misconceptions arise from flawed estimates of the size of global mineral resources which stem from a lack of understanding of the critical difference between reserves and resources. Some authors use quoted reserves the amount of metal proven to exist and to be economic for mining at present - when predicting imminent shortages. Resources - the amount that may be accessible in the upper few kilometres of the crust - are far larger.Over the last 150 years, improved technologies, economies of scale and increased efficiency have combined to reduce costs hence allowing lower-grade ore to be mined economically. The net result is that the long-term inflation-adjusted price of most metals has decreased more or less in parallel with increasing production, a second apparent paradox that frequently is not well understood.Using copper as the principal example and other metals as appropriate, we summarise the latest research on ore deposits and the activities of the minerals industry. Following a description of the numerous geological processes that form ore deposits, we outline the scientific methods used by the minerals industry to explore for new deposits. We also discuss how resources are mined and how minerals are processed, as well as recent efforts to reduce related environmental impacts. Economic and societal factors influence supply, and these are as important as the actual presence of a resource. Finally, we discuss the critical roles that geoscientists will play in assuring continued supplies of minerals. These include the development of new concepts and techniques that will assist the discovery, mining, processing, remediation, and management of mineral resources. It is essential that researchers help to educate the general public about the need for continued exploration to find new resources to meet growth in world living standards.We demonstrate that global resources of copper, and probably of most other metals, are much larger than most currently available estimates, especially if increasing efficiencies and higher prices allow lower-grade ores to be mined. These observations indicate that supplies of important mineral commodities will remain adequate for the foreseeable future.

Magmas supply metals to hydrothermal ore deposits, although typical arc basalts may be unable to produce a gold-rich ore-forming fluid, as such basalts rarely exceed 5 ppb Au. Consistent with this, the occurrence of native gold of magmatic origin is extremely rare, and only a few finds of micron-sized gold particles in unaltered basalts have been documented. Surprisingly, some lava flows and scoria cones of the historic basaltic eruptions of Tolbachik volcano (Kamchatka) are unusually gold-rich. Tolbachik basalts contain up to 11.6 ppb Au based on whole rock analyses, nuggets of gold (electrum) up to 900 μm in size and native gold droplets up to 200 μm, plus numerous vapor-deposited gold crystals within fumarolic incrustations and directly on surfaces of basaltic lapilli. Our results demonstrate that the gold nuggets in Tolbachik basalt are of hydrothermal origin and were physically scavenged from epithermal veins hosted by country rocks during intrusion of mafic magmas. Depending on the melt temperature and/or time span of the melt-rock interaction, gold was ejected by the erupting volcano either in the form of abraded nuggets or liquid droplets, or was fully assimilated (dissolved) into the shallow long-lived magma chamber to provide a 4-fold increase in gold content over background concentration of 2.7 ppb Au, characteristic of mafic volcanic rocks in Kamchatka. Upon the end of the eruption, the continued discharge of volcanic vapors enriched in gold deposited abundant crystals of gold on cooling lava and scoria. Similar to Tolbachik, recycling of metals from prior accumulations (ore deposits) in the shallow crust may take place in other long-lived magma reservoirs, thus upgrading the gold and other metal contents and contributing to the ore-forming potential of a magma.

Other| March 01, 2015 Acceptance of the Society of Economic Geologists Ralph W. Marsden Award for 2013 Jeffrey W. Hedenquist Jeffrey W. Hedenquist Search for other works by this author on: GSW Google Scholar Economic Geology (2015) 110 (2): 585. https://doi.org/10.2113/econgeo.110.2.585-a Article history first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Jeffrey W. Hedenquist; Acceptance of the Society of Economic Geologists Ralph W. Marsden Award for 2013. Economic Geology 2015;; 110 (2): 585. doi: https://doi.org/10.2113/econgeo.110.2.585-a Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEconomic Geology Search Advanced Search Madame President, SEG members and guests: I thank Larry Meinert for his citation for the SEG Ralph W. Marsden Award, both for what he said and what he left unsaid. It was Sam Adams who, as chair of the Committee on Committees, invited me to work on the SEG Membership Committee under the leadership of Bruce Bouley back in the early 1990s. This was the time when SEG had committed to build membership worldwide after its only period of membership decline, which followed the industry downturn of the late 1980s. The appointment was my first service to SEG, and it... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.