Gold Mineralization Event Research Articles

LA-ICP-MS U-Pb geochronology, trace elemental and Lu-Hf isotopic geochemistry of hydrothermal zircons in the Xiadian gold deposit, eastern North China Craton: Implications for the timing of gold mineralization and the origin of ore-forming fluids

The eastern North China Craton is characteristic of Mesozoic cratonic destruction and largescale gold mineralization. Previous geochronological studies by 40Ar–39Ar dating on alteration minerals such as sericite and K-feldspar and Rb–Sr and 40Ar–39Ar dating on quartz and pyrite suggested that the gold mineralization occurred in Early Cretaceous. We have identified hydrothermal zircons from the orebody and alterated rocks in the Xiadian gold deposit, Jiaodong Peninsula. These zircons contain two phase (vapor-liquid) fluid inclusions or enclose hydrothermal alteration minerals such as sericite. They show homogeneous low CL-response image and have high U with low Th/U, and also show enriched and flatter normalized LREE pattern with high La and low (Sm/La)N and Ce/Ce* relative to magmatic zircons. Their petrographical, textural and compositional features strongly suggest that they mainly crystallized from the hydrothermal fluids during the pyrite–sericite–quartz alteration that was closely related to the gold mineralization. Direct LA-ICP-MS U-Pb dating on such hydrothermal zircons indicates that the gold mineralization in the Xiadian deposit mainly occurred during the Paleocene and underwent a prolonged metallogenic process (68.7–56.7 Ma), most likely commenced at the end of Cretaceous and lasted at the end of Paleocene. In-situ Hf isotopic compositions of the hydrothermal and inherited zircons suggest that the ore-forming fluids might have been derived from an enriched lithospheric mantle, followed by interacting with Archean metamorphic basement during ascent. Such a gold mineralization event might have been associated with the early Cenozoic uppermost lithospheric thinning in eastern North China Craton. It has important implications for further understanding the geneses and the geodynamics of gold deposits in the whole eastern North China Craton.

Geochronological framework of the Damoqujia gold deposit, Jiaodong Peninsula, China: Implications for the timing and geologic setting of gold mineralization

The Damoqujia gold deposit in the Jiaodong Peninsula in eastern China contains more than 60 t of gold and is hosted mainly by Mesozoic granitoids. The orebodies comprise pyrite–sericite–silica altered rocks and exhibit Jiaojia‐type mineralization. Although the Damoqujia deposit is an important gold producer in the Zhaoping Fault Zone, the age and tectonic setting of metallogenesis are poorly constrained. Here, we employ precise U–Pb dating of zircon and 40Ar/39Ar dating of hydrothermal sericite from the Damoqujia gold deposit to constrain the age of mineralization, which we integrate with previous studies to understand the tectonic setting of the deposit. The major intrusions exposed in the deposit are the Jurassic monzogranite to the west and the Cretaceous granodiorite to the east. Uranium–Pb dating of zircon from the monzogranite, granodiorite, pre‐ore hydrothermally altered lamprophyre dyke, and post‐ore unaltered gabbro–diorite dyke yield concordia ages of 160 ± 1, 130 ± 1, 125 ± 1, and 120 ± 1 Ma, respectively. Based on these geochronological data, we suggest that the age of gold mineralization at Damuqujia occurred at 124–121 Ma. Sericite from the auriferous quartz–pyrite veinlet in the Damoqujia deposit yields a plateau age of 122.8 ± 0.9 Ma, representing the precise age of gold mineralization. Our geochronological data indicate that gold mineralization occurred at 123 Ma and are consistent with the timing of the main gold mineralization event in the Jiaobei Terrane at 125–120 Ma. The geodynamic setting of the study area during this time is generally considered to have been dominated by subduction of the Palaeo‐Pacific Plate beneath the Eurasian continent, with accompanying lithospheric delamination, asthenospheric upwelling, and intense craton destruction. The gold mineralization at Damoqujia was closely associated with continental extension during the Mesozoic.

Fingerprinting multiple gold mineralization events at the Dome mine in Timmins, Ontario, Canada: Trace element and gold content of pyrite

The Dome mine is host to over 16 Moz of orogenic gold deposited during a period of up to 25 Ma through multi-stage enrichment. The earliest economic stage of veining is an extensive set of ankerite veins which were historically considered barren except where overprinted by subsequent veining events. Gold in these veins is intimately associated with pyrite mineralization, and three stages of pyrite growth have been identified (Py1,2,3). The trace element content of each stage of pyrite growth determined by dynamic-secondary ion mass spectrometry and synchrotron radiation x-ray fluorescence reveals that there were three auriferous fluid events, each with a unique gold and trace element fingerprint which can be related to deposits wide mineralization events. Early ankerite vein forming fluids were auriferous, lower temperature (200–250 °C) and deposited Py1 enriched in gold, metals and metalloids (As, Cu, Ni, Zn). Py2 growth is related to deposit wide quartz-tourmaline and quartz-fuchsite veining based on trace element geochemistry, Au:Ag, and associated mineral assemblages. This deposited Ni enriched pyrite, tellurides, galena, and gold with anomalously high Au:Ag ratios. There is also evidence for remobilization of early gold and trace elements from Py1 pyrite during the Py2 forming event. The final stage of gold endowment in the ankerite veins is related to a deposit (and camp) wide quartz veining event. Py3 growth is trace element (As, Ni, Cu) and Au poor with respect to Py1 and Py2, however, this veining event contributed the bulk of the ankerite vein gold endowment. The remobilization of gold and trace elements from sieve textured Py1 in addition to overprinting Py2 and Py3 and their associated gold endowments helps explain the difficulty in applying bulk rock trace element vectors to gold at the Dome mine. The work also provides conclusive evidence for the auriferous nature of early ankerite veining at the Dome mine, and reveals that the system was fertile for a period of over 7 to 25 Ma, a key component for the formation of a world-class deposit.

The 40Ar/39Ar dating of quartz: new insights into the metallogenic chronology of the Jinchang gold deposit and its geological significance

The Jinchang gold deposit has been extensively studied, but precise dates for its formation are debated. Native gold mainly occurs as inclusions within pyrite and quartz. In this study, we analysed quartz crystals coeval with gold precipitation from two different types of mineralization using the ArgusVI multi-collector noble gas mass spectrometer by the stepwise crushing technique to resolve the timing and genesis of gold mineralization. 40Ar/39Ar dating of quartz samples (J12Q) from breccia ore yields a plateau age of 109.87 ± 0.86 Ma, and an inverse isochron age of 109.87 ± 0.88 Ma. Quartz samples (J18Q) from vein ore yields a slightly younger plateau age of 107.76 ± 0.85 Ma, with an inverse isochron age of 107.76 ± 0.92 Ma. These dates place the ore-forming age of the Jinchang gold deposit at 107~110 Ma, much younger than previously published radiometric ages, suggesting the gold mineralization is spatio-temporally associated with the granite porphyry. The formation of the Jinchang gold deposit is consistent with the regional late Mesozoic porphyry-epithermal gold mineralization event in the Yanbian-Dongning area. Finally, our study shows that 40Ar/39Ar of quartz can be used as a powerful tool to date the formation ages of hydrothermal ore deposits.

Repeated syn- and post-orogenic gold mineralization events between 1.92 and 1.76 Ga along the Kiistala Shear Zone in the Central Lapland Greenstone Belt, northern Finland

The Central Lapland Greenstone Belt (CLGB) is well endowed with orogenic gold deposits along major shear zones and structural lineaments. In the northern part of the belt, the Kiistala Shear Zone (KiSZ) hosts the Suurikuusikko gold deposit (Kittilä Mine), currently the largest gold producer in Europe. The Iso-Kuotko deposit is located 10 km to the north of Suurikuusikko along the same shear zone. Gold mineralization at Iso-Kuotko formed in two major stages: an early stage refractory gold mineralization with auriferous arsenopyrite with similarities to the ore at Suurikuusikko and a late, main stage mineralization with free gold in carbonate-quartz veins with abundant pyrrhotite, native bismuth and other sulphide minerals. This latter ore is absent at Suurikuusikko. Based on U-Pb dating, as well as Re-Os and Pb-isotope systematics of rock-forming and hydrothermal minerals, we evaluate the relationships between tectonic evolution and formation of gold deposits throughout the late Palaeoproterozoic in the northern part of the CLGB.Results from in situ U-Pb dating of zircon and petrographically well constrained hydrothermal monazite and xenotime by LA-ICPMS, and model age calculations using Re-Os isotopic data for arsenopyrite and in situ Pb-isotope data for galena from the Iso-Kuotko deposit provide evidence for multiple episodes of hydrothermal activity along the KiSZ. Data suggest coincident felsic magmatism and structurally controlled fluid flow events during wrench fault-dominated N-S shearing associated with early, micro-continent accretion ushering in the Svecofennian orogeny. This includes the formation of refractory gold ores at Suurikuusikko (1916 ± 19 Ma) and Iso-Kuotko (>1868 ± 15 Ma). Subordinate barren veining took place at ∼1830 Ma during transient extension between the accretion and final collision stage. Xenotime in late stage veins with visible gold at Iso-Kuotko yield U-Pb ages between 1761 ± 9 and 1770 ± 7 Ma. This time-interval is concurrent with widespread granitoid emplacement at the close of the Svecofennian orogeny. Disturbance of the Re-Os system in the early auriferous arsenopyrite can be connected to the late stage mineralizing processes. Pb isotope data suggest a mixed mantle and lower crust origin for fluids in the post-orogenic hydrothermal system.In situ U-Pb dating in polished thin sections in tandem with electron microprobe analyses of mineral compositions and detailed textural observations, highlights the utility of xenotime and monazite as robust geochronometers capable of recording repeated hydrothermal events in Paleoproterozoic orogenic systems. Results provide precise temporal constraints for orogenic gold mineralization and vital information to refine the tectonic evolution of the Central Lapland Greenstone Belt.

Geology, geochemistry, and geochronology of the Laozuoshan gold deposit, Heilongjiang Province, Northeast China: implications for multiple gold mineralization events and geodynamic setting

The Laozuoshan gold deposit, located in the central part of the Jiamusi Massif, is hosted by the contact zone between granitic complex and Proterzoic strata. In this study, we present the results of geochronology and geochemistry of ore-related granodiorite and diorite porphyry, and hydrothermal sericite 40Ar/39Ar dating. The granodiorite and diorite porphyry in the Laozuoshan gold deposit are calc-alkaline and high-K (calc-alkaline) series, which are enriched in LREE and LILE and depleted in HFSE, with no depletion of Eu. The geochronology data show that zircon U–Pb ages of the granodiorite and diorite porphyry are ∼262 Ma and ∼105 Ma, respectively. The sericite 40Ar/39Ar ages are ∼194 Ma and ∼108 Ma. On the basis of previous researches, ore geology and geochronology studies show that the Laozuoshan gold deposit underwent at least two gold mineralization events. We suggest that the first one, which was related to skarnization, resulted from the collision between the Jiamusi and Songnen Massifs in Late Permian. The subsequent gold mineralization resulted from the subduction of the paleo-Pacific Plate in Early Cretaceous.

La Colosa Au Porphyry Deposit, Colombia: Mineralization Styles, Structural Controls, and Age Constraints

The La Colosa porphyry Au deposit is located on the eastern flank of the Central Cordillera of Colombia, within the Middle Cauca metallogenic belt. The deposit contains more than 800 t (22.37 Moz) Au at grades up to 0.8 g/t and is hosted by a composite porphyry stock of dioritic to tonalitic composition, which was emplaced into Triassic-Cretaceous schists of the Cajamarca Complex in the late Miocene (~8 Ma). The country rocks underwent two ductile deformation events, including development of shear zones, folds, and penetrative foliation, prior to emplacement of the stock. Subsequent brittle deformation reactivated preexisting N- and NNE-trending structures and formed secondary faults due to a change from right- to left-lateral shear sense on regional faults. This switch in stress orientations is attributed to a new plate configuration in the mid-Miocene. The left-lateral movement along regional faults favored emplacement of intrusive centers in dilational pull-apart zones, including the La Colosa stock within the regional Palestina fault zone. Three gold mineralization events are recognized at La Colosa. The first was of porphyry style, during which hypersaline fluids (40–50 wt % NaCl equiv) formed predominantly A- and S-type veinlets and caused multistage wall-rock silicification accompanied by potassic and sodic-calcic alteration. The early-stage intrusions contain the highest gold grades varying from 0.75 to 1 g/t Au, associated with pyrite and minor chalcopyrite, molybdenite, and magnetite in the porphyries and with pyrrhotite-pyrite-melnikovite in the country rocks. In the intermineral-stage intrusions the gold grades drop to 0.5 to 0.75 g/t Au, and pyrrhotite and pyrite are the major sulfides. Gold grades reach low values of <0.3 g/t Au in the late-stage porphyries. The second gold-precipitating event formed sheeted veinlets of drusy quartz and pyrite with centimeter-wide halos of albite-sericite-pyrite overprinting all other alteration types at the deposit. A ~200°C hydrothermal brine (21–28 wt % NaCl equiv) deposited gold at high grades (>1.5 g/t Au over >10 m drill core intervals) within N-striking normal faults that developed during and after emplacement of the porphyry stock. The third mineralization event was supergene, with Au enrichment confined to late porphyries and characterized by sulfide boxworks, resulting in gold grade increases from 0.3 to 1.2 g/t Au.

New metallogenic model of telescoped Eocene-Miocene Au-U epithermal mineral deposit in the Placer de Guadalupe district, Chihuahua, Mexico

The chronological repartition of mineral deposits in Mexico and the southern USA coincides with the distribution of the three main volcanic pulses of the Sierra Madre Occidental. These pulses are Eocene to early Miocene in age, suggesting that a broad migration occurred from northwest to southeast, where the last ignimbrite flare-up occurred. The most fertile event occurred from 36 to 28 Ma and produced all of the largest Ag-Au mining districts. The Placer de Guadalupe Au-U district contain a unique association of metals with high variations in their U/Au ratios that are not common worldwide. The uraninite population dated by Wells (1930) yielded an age of ca. 36 Ma, which is comparable to that of the volcanic intrusions and dykes dated in the district (yielding ages of ca. 36 Ma). Altered uraninite cemented by gold sheets provide an age of 21 Ma, which is interpreted to be the age of the gold epithermal event. Studies of fluid inclusions in the quartz and calcite cements formed in the gold event indicate the presence of immiscible magmatic brines and CO2. Homogenization temperatures by halite melting range from 268 °C to 305 °C and 266.6 °C to 283 °C, with salinities ranging from 35.9 to 38.9 and 36.0 to 37.5 wt% eq NaCl, in the quartz and calcite stages, respectively. C-O isotopic compositions of U and Au calcite cements suggest a trend of low-temperature alteration caused by hydrothermal fluids. These C-O isotopes suggest that during the gold event, water/rock interaction processes occurred between magmatic fluids and the carbonate host-rock. REE enrichment in the U calcite cement suggests that La-Ce enriched carbonatite volcanic formations participated in the mineralizing process. The U mineralization event was controlled by (1) a metal and heat source (in this case, late Eocene volcanism and, in particular, a carbonatite volcanic event); (2) an efficient transport mechanism for the large-scale input of meteoric water, which was channeled, heated and U-enriched into reactivated crustal Eocene faults from a deep U source to a shallow sedimentary chemical trap; (3) an effective trap, which is represented in this study by the presence of an organic matter-rich sedimentary formation. The gold mineralization event was characterized by the Miocene extensional peak coupled with asthenospheric upwelling, which facilitated the melting/metamorphism of the lower crust and the expulsion and transport of large amounts of CO2-bearing fluids to a shallow crustal level through the reactivated crustal Laramide thrust faults. The fluids’ interactions with the entire stratigraphic column, from the Grenvillian to the Late Triassic basement, favored the leaching of gold and the enrichment of CO2-bearing fluids. Gold deposition appears to be related to boiling but was ultimately favored by water-rock interaction with U mineralization and the Upper Plomosas shale. Study of the Au-U Placer de Guadalupe deposit reveals evidence of a new Miocene metallogenic event in central and northern Mexico. Its genetic relationship with the Basin and Range (BnR) and Rio Gande Rift (RGR) in USA and its transition from post-orogenic to Miocene intraplate extension in Mexico provides a new perspective regarding the exploration of Miocene gold epithermal deposits in northern Mexico and the southern USA.

Decratonic gold mineralization: Evidence from the Shangzhuang gold deposit, eastern North China Craton

The Jiaodong Peninsula in the eastern North China Craton (NCC) hosts some of the world-class gold deposits. Among these, the Shangzhuang gold deposit represents a typical fault-zone hosted disseminated- and stockwork-style gold mineralization. The mineralization is characterized by intense hydrothermal alteration halos in the wallrocks with the mineralized veins intruding into altered wallrocks. Zircon U-Pb isotope dating constrains the timing of emplacement of the Guojialing granodiorite as 130±1Ma. Five molybdenite samples from the main mineralization stage veins yielded a well-fitted isochron age of 126±2Ma (MSWD=1.3), marking the timing of gold mineralization. Four types of fluid inclusions are identified at Shangzhuang, and their petrographic and microthermometric features suggest fluid immiscibility followed by fluid mixing. This inference is also supported by oxygen and hydrogen isotopic data of quartz veins from stage III. The measured δ18O values of quartz are +12.3 to +13.7‰ for stage II and +11.7 to +12.0‰ for stage III, with calculated δ18Ofluid values for stage II ranging from +5.9 to +7.3‰ and for stage III from +3.4 to +3.7‰. δD values for stage II and III quartz range from −65.3 to −75.2‰ and −70.6 to −74.7‰, respectively. The data suggest that the ore-forming fluids were initially derived from magmatic sources, followed by mixing with meteoric water. SIMS in-situ sulfur isotope analyses of two types of pyrite (Py I and Py II) from different mineralization stages show different sulfur isotope features. The δ34S values for Py I (+10.2 to +11.3‰, mean=+10.8‰, n=25) are higher than those of the later mostly gold-related Py II (+4.1 to +6.8‰, mean=+5.4‰, n=27). The higher δ34S values of Py I are correlated to degassing of mantle wedge metasomatized by the slab fluids. The relatively lower δ34S values of Py II might suggest increasing of fO2 through fluid mixing between ore-forming fluids and meteoric water.The temporal, spatial and tectonic relations between the giant gold mineralization and destruction of the NCC suggest a genetic linkage. The gold mineralization between 126 and 117Ma at Jiaodong was probably initiated at the peak of decratonization (ca. 125Ma) of the eastern NCC. Phanerozoic craton margin orogeny also played a critical role in the generation of the early Cretaceous giant gold deposits in the eastern NCC. Integrated geological characteristics, mineralization features, metallogenic age, sources of ore-forming fluids and sulfur, and tectonic settings favor a decratonic gold mineralization model for the Shangzhuang gold deposit. The geodynamic scenario proposed for the early Cretaceous giant gold mineralization event in the eastern NCC includes the paleo-West Pacific plate subduction, asthenospheric upwelling, multiple subduction-collision processes along the margins.

40Ar/39Ar dating of the Jiehe gold deposit in the Jiaodong Peninsula, eastern North China Craton: Implications for regional gold metallogeny

The Jiehe gold deposit, containing a confirmed gold reserve of 34 tonnes (t), is a Jiaojia-type (disseminated/stockwork-style) gold deposit in Jiaodong Peninsula. Orebodies are hosted in the contact zone between the Jurassic Moshan biotite granite and the Cretaceous Shangzhuang porphyritic granodiorite, and are structurally controlled by the NNE- to NE-striking Wangershan-Hedong Fault. Sulphide minerals are composed predominantly of pyrite with lesser amounts of chalcopyrite, galena, and sphalerite. Hydrothermal alteration is strictly controlled by fracture zones, in which disseminated sulfides and native gold are spatially associated with pervasive sericitic alteration. Mineralogical, textural, and field relationships indicate four stages of alteration and mineralization, including pyrite-bearing milky and massive quartz (stage 1), light-gray granular quartz–pyrite (stage 2), quartz–polysulfide (stage 3) and quartz–carbonate (stage 4) stages. Economic gold is precipitated in stages 2 and 3.The Jiehe deposit was previously considered to form during the Eocene (46.5±2.3Ma), based on Rb-Sr dating of sericite. However, 40Ar/39Ar dating of sericite in this study yields well-defined, reproducible plateau ages between 118.8±0.7Ma and 120.7±0.8Ma. These 40Ar/39Ar ages are consistent with geochronological data from other gold deposits in the region, indicating that all gold deposits in Jiaodong formed in a short-term period around 120Ma. The giant gold mineralization event has a tight relationship with the extensional tectonic regime, and is a shallow crustal metallogenic response of paleo-Pacific slab subduction and lithospheric destruction in the eastern NCC.

A possible genetic relationship between orogenic gold mineralization and post-collisional magmatism in the eastern Kunlun Orogen, western China

Controversies in orogenic gold deposits remain, especially regarding the relative contribution of magmatic fluids to the mineralization. The Shuizhadonggou-Huanglonggou gold deposit in the Wulonggou gold field of the eastern Kunlun Orogen, western China consists mainly of sulfide disseminations in hydrothermally altered rocks with minor amounts of quartz-sulfide veins coeval to or overprinting the disseminated ores. Gold mineralization is hosted in diverse lithologies (i.e., Early Palaeozoic metamorphic rocks, Late Silurian syenogranite and Late Triassic porphyritic granodiorite and quartz diorite) and is structurally controlled by a second-order NW-trending sinistral-normal ductile shear zone and its subsidiary structures along the first-order Central Kunlun Fault. Gold-related hydrothermal alteration formed chlorite, sericite, quartz and calcite, with associated sulfide minerals dominated by pyrite, arsenopyrite, löllingite and pyrrhotite. Two types of hydrothermal sericite separates from a gold mineralized syenogranite yielded two 40Ar/39Ar ages of 237.0±2.0Ma and 230.8±1.7Ma, respectively, which postdated the Early Triassic regional metamorphism and ductile deformation by ~13m.y. Field relationships suggest that gold mineralization also overprinted ~220Ma porphyritic granodiorites and quartz diorites. These data indicate three gold mineralization events in the Late Triassic overlapped with post-collisional magmatism in the orogen. Gold-bearing sulfides have δ34S values mostly in the range of 2.0–5.5‰, consistent with a magmatic source of sulfur. Quartz from quartz-pyrite-sericite veins has calculated δ18OH2O values of 1.8–6.1‰ and δDH2O of −63 to −107‰. The stable isotopic and geochronological data suggest a magmatic origin for the ore-forming fluids. Therefore, the Shuizhadonggou-Huanglonggou and other gold deposits in the eastern Kunlun Orogen share many features of orogenic gold deposits (e.g., multiple-order ore-controlling structures, hydrothermal alteration, mineralization styles, close association between mineralization and magmatism, and H-O-S stable isotope compositions) and are genetically related to Late Triassic post-collisional magmatism.

Structural Constraints and Localization of Gold Mineralization in Leather Jacket Lodes, Ballarat, Victoria, Australia

Gold mineralization at the Ballarat East deposit, central Victoria, Australia, is hosted in lodes that are historically known as “leather jackets.” These are quartz-dominant vein arrays related to low-displacement, W-dipping faults (≤45°) that transect the core and/or eastern limb of tight, asymmetric N-S-trending anticlines. The leather jacket lodes typically have dip extents from 5 to 65 m, widths of ≤20 m, and strike lengths up to hundreds of meters, but their along-strike continuity is disrupted by oblique, low-displacement listric faults known as “cross courses.” The gold lodes are characterized by distinct phases of sulfide paragenesis with minor gold + arsenopyrite + pyrite defining the early sulfide stage. Late-stage coarse gold was precipitated with galena + sphalerite ± pyrrhotite ± chalcopyrite (late pyrite also occurs). The gold mineralization events are linked to low-strain mineralized fracture networks, which are closely related to the final deformation stages and the amplification of the major folds enclosing the lodes. This amplification produced domal fold culminations, with plunges ≤30°, and localized minor parasitic folds with shallower plunges (≤10°). A network of dilation sites, on the W-dipping faults, preferentially developed in the cores of anticlines, particularly in zones where there are changes in strike of bedding or fault bifurcation and refraction through contrasting sandstone and interbedded packages of sandstone and shale. Numerical three-dimensional simulations were undertaken to test our geologic observations and replicate conditions controlling the emplacement of the leather jacket lodes. Two different scenarios were investigated: first, to determine how changes in the local stress field orientation influences dilation and fluid infiltration; secondly, to test variations in fault geometry during the last stages of deformation—that is, within the final 2% of shortening, when most of the mineralized sites were created. Results show that strain and fluid flow localized along refracted sections of faults and around changes in dip, specifically on the shallower dipping sections within subvertical sandstone units. This is consistent with the observation that high-grade gold-bearing quartz is associated with localized changes in fault dip in thicker sandstone and sandstone-shale packages. There was also a component of strike-slip motion and near-field NW-to-SE or N-to-S stress fields, which can be attributed to the development of a component of out-of-plane motion during the development of fold culminations. The preferred model for the distribution of the high-grade auriferous vein arrays defining the leather jacket lodes is one of fold amplification and extension parallel to the fold axes, which produced an increasing out-of-plane relaxation. The main fluid conduits responsible for the leather jacket style of mineralization involve infiltration along steep bedding-parallel faults and veins that link up with the arrays of low-displacement W-dipping faults.

Tectonic evolution of the Gaoua region, Burkina Faso: Implications for mineralization

The interpretation of high-resolution airborne geophysical data integrated with field structural and lithological observations were employed in the creation of a litho-structural framework for the Gaoua region, Burkina Faso. The granite-greenstone domain of Paleoproterozoic age was affected by multiple deformation and mineralization events. The early tectonic phase is characterized by the emplacement of voluminous tholeiitic and calc-alkaline lavas, probably in a volcanic arc setting. The copper mineralization in Gongondy, Dienemera and Mt Biri is concentrated in a diorite/andesite breccia, and is interpreted as porphyry-copper style formed at an early stage of the evolution of the area. Evidence for the first deformation event D1Ga corresponding to N–S shortening was only found in the E–W trending mafic unit bordering the Gaoua batholith to the south. A second deformation phase D2Ga occurred under greenschist facies conditions and lead to a development of more or less penetrative metamorphic foliation and its subsequent folding under overall E–W compression. At later stages, the D2Ga switched to a transcurrent regime characterized by intense N–S to NW-trending steeply dipping shear zones. The first significant gold mineralization event is related to this transcurrent tectonic phase. During subsequent D3Ga, intense network of brittle to brittle–ductile NW and NE faults developed. Economic gold concentrations are attributed to the D3Ga event and are associated with the remobilization of early disseminated low grade gold concentrations. Significant deposits in the area are Nassara, Gomblora, Batié West and Kampti. The last deformation event D4Ga resulted in E–W trending thrust faults and crenulation cleavage planes, under overall N–S compression. No mineralization events related to this stage have been seen.

Discussion: The timing of gold mineralization across the eastern Yilgarn Craton using U–Pb geochronology of hydrothermal phosphate minerals

The presentation of recent geochronological work on orogenic gold deposits in the Eastern Goldfields of the Yilgarn Craton, Western Australia, claims to prove that there is a single broad event of gold mineralization and that structural work demonstrating that there are a number of discrete gold mineralization events is wrong. This new data demonstrates no such thing, as this data, no doubt the best that can currently be produced, shows a very wide and inconsistent range in ages. Geochronology is not yet able to reliably separate these events, which appear to be spread over an interval of perhaps 30 Ma, up to ∼2635 Ma.

Decratonic gold deposits: a new concept and new opportunities

Early Cretaceous gold deposits in the North China Craton and the famous Carlin-type gold deposits in Nevada are given the name ‘decratonic gold deposits’ [1]. This is the first new type of ore deposit proposed in the last 20 years. This new type of deposit introduces a concept that may change perspectives and provide fresh opportunities for gold deposit research and exploration. Cratons are stable ancient crustal domains characterized by thick lithospheric mantle roots (>150 km), weak tectonism, and little or no magmatic activity within their boundaries. Since their stabilization, the formation of endogenic mineral deposits in such ancient cratonic blocks is very rare owing to a lack of significant magmatism, deformation, or generation of hydrothermal fluids. Several cratons, however, including the North China, the North American and the Brazilian cratons, have experienced destruction to differing degrees [1]. The eastern part of the North China Craton was extensively destructed in the Early Cretaceous [2]. Meanwhile, gold deposits with a total reserve of 4000– 5000 tons formed there within a few millionyears (130–120Ma), coevalwith craton destruction [1]. Similarly, the western part of the North American Craton was destabilized in theCenozoic and that destructionmay be responsible for the famous Nevada Carlin-type gold deposits that host a total of over 6000 tons of gold reserves [1,3]. It is suggested that all these deposits nowbe termed ‘decratonic type’ gold deposits, deposits formed by magma-derived fluids under extensional tectonics conditions associated with craton destruction [1]. The model further postulates that the westward subduction of the western Pacific Plate in the Early Cretaceous and the eastward subduction the eastern Pacific Plate in the Cenozoic were responsible for these twomajor gold mineralization events. Dehydration of the subducted and stagnant slabs led to continuous hydration andmetasomatism of the overlying mantle wedges and the enrichment of gold and other chalcophile elements. Subsequent partial melting of the mantle wedge produced ore-forming fluids (Fig. 1) [1]. Gold deposits in the North China Craton have been classified into two types: ‘altered-rock’ type and ‘quartzvein’ type. The altered-rock-type gold deposits are characterized by disseminated and stockwork goldmineralization, which is usually controlled by brittle or ductile to brittle fault zones. These types of deposits have commonly been intensively overprinted by hydrothermal alteration and suffered later brittle deformation. The quartz-vein-type gold deposits are hosted in the Archean amphibolite facies rocks or earlier granitoids and typically have large proportions of visible native gold. In contrast, the Carlin-type gold deposits in Nevada typically contain invisible gold hosted in fine-grained sulfides disseminated in Paleozoic marine sedimentary rocks.The North China Craton and Carlin gold deposits are seemingly entirely different, but both types are genetically related to craton destruction. Carlin-type gold deposits are abundant in Nevada but have not been found in the North China Craton. The decratonic gold deposit model ascribes the contrast in mineralization styles to host rocks, controlling structures, and ore-forming depths [1]. Decratonic gold deposits in both the North China Craton andNevada formed within a relatively short time interval (<10Ma). In both areas, the deposits become progressively younger toward the subduction zones. Such temporal trends may plausibly be explained by subduction retreat or rollback of the subducted slab at rates of 8.8 and 3.3 cm y−1 for the western and eastern Pacific plates, respectively [1]. Craton destruction starts deep in the mantle with mantle-derived melts and fluids, implying that decratonic gold deposits may extend to great depths. This suggests newopportunities for future discoveries. It is proposed that gold mineralization belts extending approximately NNE in the eastern and the western portions of the Eastern Block of the North China Craton are the most favorable areas for future exploration [1]. ‘Decratonic gold deposit’ is a new term. It will inevitably face reactions that will affirm or challenge it, and that may improve or refute it. Major questions are: the (paleo)-Pacific plate has subducted westward underneath the whole of east China followed by slab rollback during three periods since the Jurassic [4,5].Why did goldmineralization in the North China Craton take place mainly within a short period in the Early Cretaceous? Episodes of tectonic extensions in the North China Craton also have lasted for long periods. What made the Early Cretaceous so different? If craton destruction was the controlling factor, then what made craton destruction unique? Alternatively, are craton

The timing of gold mineralization across the eastern Yilgarn craton using U–Pb geochronology of hydrothermal phosphate minerals

The highly mineralized Eastern Goldfields of the eastern Yilgarn craton is an amalgamation of dominantly Neoarchaean granitoid-greenstone terranes and domains that record a history of early rifting, followed by westward directed collision with initial arc formation, collision and clastic basin formation, and final accretion to the western Yilgarn proto-craton between 2.66 and 2.60 billion years ago. The gold deposits that define this region as a world-class gold province are the product of orogenic processes that operated during accretion late in the tectonic history, after initial compressional deformation (D1–D2) and the majority of granitoid magmatism. Minor gold was also deposited throughout the entire tectonic history in magmatic-hydrothermal-related systems. However, such mineralization (mostly < 0.3 g/t gold) is nowhere economic unless it overprints, or is overprinted by, much higher-grade orogenic gold lodes. Robust SHRIMP U–Pb geochronology of gold-related hydrothermal xenotime and monazite supports structural studies that gold mineralization occurred during late transpressional events (D3–D4), shortly before cratonization. However, westward migration of collision and accretion produced a complementary diachroneity in the timing of gold mineralization of 5 to 20 m.y. between c. 2.65 Ma in the east (including Laverton District, Kurnalpi Terrane) to c. 2.63 Ma in the west (including Kalgoorlie Terrane) across the eastern part of the craton. The robust geochronology refutes previous suggestions that significant gold mineralization events extended from DE to D4 in the evolution of the orogen and that the Kalgoorlie gold deposits formed over a period of 45 m.y. The crustal continuum model is applicable within terranes where orogenic gold depositional events were penecontemporaneous, but must be modified to account for diachroneity of orogenic events and gold mineralization across the Eastern Goldfields.

The Wassa deposit: A poly-deformed orogenic gold system in southwest Ghana – Implications for regional exploration

The Ashanti greenstone belt in southwest Ghana hosts many gold deposits distinguished by different timing and structural contexts. This study investigates the evolution of the Wassa system by integrating field and geophysical observations. This 4 million ounces (past production and current resources) gold deposit is interpreted to represent the oldest gold mineralization event in West Africa with gold-bearing pyrites aligned and stretched within the S1 ductile fabric. Mineralized quartz-carbonate veins were strongly deformed during the D1 deformation event. Three additional folding events are characterized by hectometer-scale tight to isoclinal folds, by a kilometer-scale synform fold centered on the mine and by a late recumbent metric-scale folds. Because of its early timing, the Wassa system represents a new poly-deformed deposit type in West Africa and highlights a potential for new discoveries in the underexplored meta-volcanic and meta-sedimentary Sefwi Group. Timing of the gold mineralization at the Wassa mine makes this deposit type a possible candidate for the source of the gold contained in the Tarkwa paleoplacer.

Geology and ore genesis of the Yu'erya gold deposit, eastern Hebei Province, China

The large Yu'erya gold deposit (65t of contained gold averaging 2.3g/t Au) in the eastern part of the Hebei Province of China is spatially associated with the Yu'erya Granite, and a group of NE- and NNE-trending faults. The alteration associated with mineralization is characterized by the assemblage pyrite, quartz, sericite, albite, and carbonate. Four stages of mineralization, in chronological order, are (1) quartz and medium- to coarse-grained pyrite; (2) quartz, fine-grained pyrite, and gold; (3) quartz, polymetallic sulfide, tellurobismuthite, and gold; and (4) quartz, pyrite, and carbonate. Most of the gold was deposited during the second and third stages of alteration from mesothermal fluids. These fluids were relatively rich in H2O, CO2, K+, Ca2+, Cl, and S, and low salinity. The H–O and sulfur isotope ratios determined for the mineralized samples indicate a magmatic source, and the Pb isotope data indicate that the Au mineralization originated from the mantle and lower crustal materials. Geochronological data indicate that the gold mineralization event was restricted to 200–163Ma whereas the associated magmatism occurred between 200 and 150Ma. This Mesozoic gold mineralization is related to the subduction of the Mongolia–Okhotsk and Paleo-Pacific oceans along the edges of the North China Craton.

Re–Os geochronological constraints on the Dabolava mesothermal gold occurence, Madagascar: Implications for the Ikalamavony sub-domain deposition age

New Re–Os ages for early concordant veins and later discordant veins in the Ikalamovony sub-domain of west-central Madagascar require respectively a Paleoproterozoic age for metasedimentary rocks and a Pan-African age for the orogenic type occurrences. Indeed, this paper focuses on Re–Os geochronology of Dabolava gold occurrences, located in the Ikalamavony sub-domain, western central part of Madagascar. Two types of gold veins have been identified in this region; (i) type 1, centimetre-thick quartz veinlets, with diffuse contacts and concordant to the main regional foliation of the host amphibolites, part of the upper-Group of the Ikalamavony sub-domain; (ii) type 2, 30–50cm-thick quartz veins variously transposed in shear zones affecting the Dabolava granodioritic orthogneisses, part of the Dabolava magmatic suite. These two types of veins with Au–Py assemblages have been sampled for Re–Os geochronology. The type 1 pyrite and electrum assemblage yields a Palaeoproterozoic age (1961±79Ma) whereas the pyrite and electrum assemblage of discordant type 2 veins yields a Pan-African age (533±23Ma). These ages record two main gold mineralization events that affected this crustal segment. Assuming that the Re–Os systematics were not perturbed by more recent events, the 1961±79Ma age obtained in this study on type 1 gold vein concordant in amphibolites favours a Palaeoproterozoic deposition age for the whole Ikalamavony sub-domain, both lower- and upper Groups. This age contrasts with the previously proposed Mesoproterozoic age for the deposition of the upper Group of the Ikalamavony sub-domain but is consistent with the Paleoproterozoic age (∼1800Ma) deduced from detrital zircon ages in the Ikalamavony quartzites located in the Ikalamavony lower Group. The Pan-African age obtained on the type 2 gold deposits is much younger than the emplacement age of the host granodiorite and precludes a porphyry-type model for this gold mineralization and rather favours an orogenic type with a deposition during the Pan-African orogeny.

Structural and hydrothermal alteration evidence for two gold mineralisation events at the New Celebration gold deposits in Western Australia

The New Celebration gold deposits (∼2 Moz Au) are located within the Boulder segment of the first-order, transcrustal Boulder-Lefroy fault zone about 35 km southeast of Kalgoorlie, in the Kalgoorlie Terrane of the Eastern Goldfields Province, Western Australia. The gold deposits are hosted by ultramafic rocks (komatiite), differentiated gabbro/dolerite and variably thick (0.5 to 5 m, locally up to 80 m) felsic porphyry dykes that have intruded the ultramafic–mafic rock contact. Host rocks have undergone regional metamorphism to upper greenschist facies.At least four deformation events are recorded at New Celebration: (1) D1NC is represented by vertical stratigraphic contacts, the expression of regional scale upright folds. (2) D2NC deformation is expressed as a well-developed, NNW-trending, steeply WSW-dipping penetrative shear foliation (S2NC) and foliation-parallel, boudinaged quartz–carbonate veins (V2NC), which are representative of the regional D2 Boulder fault zone; movement on the fault is sinistral oblique slip. (3) D3NC deformation resulted in NNE-trending, WNW-dipping, short strike length (<50 m) faults, quartz–carbonate–epidote–chlorite fault fill veins and widely spaced S3NC foliation. Subhorizontal L3sNC slickenline lineations on D3NC fault planes indicate strike-slip movement during D3NC (no kinematic indicators are observed), whereas the geometry of S–C fabrics in the S3NC foliation suggests sinistral movement. (4) D4NC deformation is poorly developed by west-dipping, curviplanar faults that cross cut the S2NC foliation. Lineations formed during D2NC deformation include: (a) moderate to steep, SSE to SSW-plunging L2mNC mineral elongation lineations, (b) moderate, NW-plunging L2iNC intersection lineations between S- and C-foliation planes, and (c) moderate to steep, SSE to SSW-plunging L2sNC slickenline lineations. Moderate to steep SSW-plunging quartz L2mNC elongation lineations, in conjunction with the orientation of S–C fabrics, constrain the sense of movement on the shear zone as sinistral oblique-slip. The S2NC foliation is also developed in thin (1–5 m width) M1 plagioclase-rich porphyry dykes, thus indicating their emplacement pre- to syn-D2NC deformation. The mylonitic fabric in the first-generation Magmatic 1 (M1) porphyry dykes contrasts with the ‘fresh,’ undeformed igneous textures of second generation Magmatic 2 (M2) quartz–feldspar porphyry dyke, which preferentially intruded along the mafic–ultramafic rock contacts. The lack of internal ductile deformation fabrics and a predominance of brittle structures (e.g. fracture network at the margins) in the M2 porphyry dyke indicate its emplacement into a brittle deformation environment.Two gold events are interpreted at the New Celebration deposit. (1) An ‘early’ Mylonite-style gold event in high-strain, quartz–ankerite–biotite–sericite mylonite in mafic rocks and M1 porphyry dykes, which is interpreted to be synchronous with the D2NC deformation. Minute inclusions of gold (<100 μm) are hosted within pyrite that is aligned parallel to the S2NC foliation planes. Gold in mafic mylonite is in equilibrium with ankerite–sericite ± biotite ± pyrite and is also spatially and temporarily associated with gold and non-gold-bearing tellurides such as calerverite, petzite, hessite, altaite, melonite and a bismuth telluride. (2) A ‘late’ gold event that consists of Contact and Fracture-infill styles. The Contact-style gold mineralisation is located in high-Mg basalt within S2NC foliation planes that wrap around the M2 porphyry dyke during late D2NC deformation. Gold is in equilibrium with pyrite–sericite–ankerite. TheFracture-infill-style gold mineralisation is located in brittle fracture networks formed at the margin of the M2 porphyry dyke. ‘Free’ gold and inclusions of gold in pyrite are in equilibrium with pyrite–sericite2 ± ankerite. No telluride species are observed in either Contact or Fracture-infill-style mineralisation. The exact timing of the Fracture-infill-style gold mineralisation is equivocal; it may have formed late-D2NC or during D3NC or even during a later deformation event.The New Celebration gold deposits are a rare example of an orogenic gold system located in a first-order, transcrustal fault system, the Boulder-Lefroy fault. Its complex fault zone architecture and long-lived nature of fault movement is interpreted to be at least in part responsible for the high gold endowment when compared with the typically barren first-order fault zones. Magnetite and biotite in the outer alteration zones are spatially related to M1 dykes, and the spatial and temporal restriction of tellurides to the M1 dyke suggest that the orogenic New Celebration gold deposits were sourced from magmatic fluids, at least during the early stages of the formation of the deposits.