Copper isotope constraints on the genesis of the Keweenaw Peninsula Native Copper District, Michigan, USA

The Keweenaw Peninsula native copper district of Michigan, USA is the largest concentration of native copper in the world. The copper isotopic composition of native copper was measured from stratabound and vein deposits, hosted by multiple rift-filling basalt-dominated stratigraphic horizons over 110 km of strike length. The δ65Cu of the native copper has an overall mean of +0.28‰ and a range of −0.32‰ to +0.80‰ (excluding one anomalous value). The data appear to be normally distributed and unimodal with no substantial differences between the native copper isotopic composition from the wide spread of deposits studied here. This suggests a common regional and relatively uniform process of derivation and precipitation of the copper in these deposits. Several published studies indicate that the ore-forming hydrothermal fluids carried copper as Cu1+, which is reduced to Cu0 during the precipitation of native copper. The δ65Cu of copper in the ore-forming fluids is thereby constrained to +0.80‰ or higher in order to yield the measured native copper values by reductive precipitation. The currently accepted hypothesis for the genesis of native copper relies on the leaching of copper from the rift-filling basalt-dominated stratigraphic section at a depth below the deposits during burial metamorphism. Oxidative dissolution of copper from magmatic source rocks with magmatic δ65Cu of 0‰ ± 0.3‰ is needed to obtain the copper isotopic composition of the metamorphogenic ore-forming hydrothermal fluids. In order to accommodate oxidative dissolution of copper from the rift-filling basalt source rocks, the copper needs to have been sited in native copper. Magmatic native copper in basalt is likely stable when the magma is low in sulfur. Low sulfur is predicted by the lack of sulfide minerals in the ore deposits and in the rift-filling basalt-dominated section, which are source rocks, the same rocks through which the ore fluids moved upwards, and the host rocks for the native copper ores. When combined with geologic evidence and inferences, the copper isotopic composition of native copper helps to further constrain the genetic model for this unique mining district

Revisiting "Tin in South-eastern Europe?"

Obnovom arheoloških iskopavanja antičkog kastela Timakum Minus 2019. godine stvorile su se nove mogućnosti za tumačenja njegovih građevina koje su istraživane pre više decenija. Među ostacima građevina oko antičkog kastela Timacum Minus-a posebnu pažnju privlači delimično istražen "objekat sa hipokaustom", naročito u pogledu njegovih konstruktivnih karakteristika. Pored inače čestih antičkih konstrukcija hipokausta i zidnog grejanja, među ostacima ove građevine uočena je i posebna vrsta građevinskih elemenata - keramičke cevi za svodove. Velika količina otkrivenih cevi ukazala je na to da je ova građevina zaista imala svodove izrađene od njih. Iako je pojava cevi za svodove prilikom istraživanja antičkih lokaliteta na tlu jugoistočne Evrope registrovana, ona nije dovoljno dokumentovana, kao što ni sama funkcija cevi često nije prepoznata. Jedan od razloga za to jeste nedovoljna upućenost istraživača u specifične karakteristike cevi za svodove i njihovu funkciju, usled čega se one mešaju sa vodovodnim cevima, tubulusima ili kalemovima vezanim za zidno grejanje - budući da svaki od tih elemenata pripada keramičkim proizvodima koji su namenjeni građevinarstvu. U radu su razmatrane karakteristike cevi za svodove na Timakum Minusu, kao i kontekst u kome su pronađene unutar "objekta sa hipokaustom". Na osnovu nalaza pečata kohorte Aurelije II Daradanorum određeno je da "objekat sa hipokaustom" i konstrukcija svodova od keramičkih cevi potiču iz III veka - u kome je i inače pojava tih svodova širom Rimskog carstva bila česta. Prilikom sistematizacije vrsta keramičkih cevi na Timakum Minusu posebno je izdvojena ona koje je bilo najviše u "objektu sa hipokaustom". U sklopu nje je prepoznat i sasvim specifičan centralni element koji je omogućavao da se dva niza cevi na istom pravcu, ali iz suprotnih smerova, međusobno spoje. Taj element je definisao oblik svoda kojim su bile pokrivene prostorije čiju je rekonstrukciju osnove bilo moguće izvršiti. Arhitektonske analize "objekta sa hipokaustom", kao i karakteristike uočene na samim cevima ukazale su na to da su prostorije bile pokrivene poluobličastim svodom, izgrađenim od lučnih vertikalnih nizova cevi koje su u temenu bile ,,zaključane" centralnim elementom. Rekonstrukcija izgleda cevi i načina njihovog ređanja uklapa se u hronologiju izvođenja objekta i svoda tokom III veka. Daljim statičkim analizama došlo se do još nekoliko saznanja. Pokazalo se da je preko svoda morao biti nanesen određen sloj malterne mase da bi debljina svoda dosegla optimalnu vrednost u opsegu 20-30 cm. Na osnovu proporcija objekta koje su određene u njegovoj osnovi ispitana je visina objekta, gde je grupa slučajeva takođe definisana proporcionalno. Prema našim analizama, zidovi prostorija "objekta sa hipokaustom" u kojima su cevi registrovane mogli su dosezati visinu do 3,08 m, dok je visina prostorija u temenu svoda mogla biti 6,16 m. Ovim istraživanjem pokušali smo da ukažemo na veliki značaj pojedinačnih arhitektonsko-građevinskih elemenata, a među njima i keramičkih cevi za svodove, kojima se često ne pridaje dovoljna pažnja. Nalazi keramičkih cevi za svodove u Timakum Minusu, uz izvršene arhitektonske analize, upotpunjuju sliku otkrivenog "objekta sa hipokaustom" iz više aspekata. Posebno je značajno definisanje njegove visine, koje je veoma teško za antičke građevine profane arhitekture na našem tlu budući da su najčešće sačuvane u prizemnoj ili temeljnoj zoni. Značaj nalaza keramičkih cevi za svodove u Timakum Minusu veliki je stoga što je on omogućio kako konkretno definisanje konteksta njihovog nalaza tako i rekonstrukciju oblika određenih delova građevine pomoću tog elementa, što do sada nije istraživano prilikom analiza antičke arhitekture na tlu jugoistočne Evrope.The important role of the Balkans in the origin and development of metallurgy is well established with respect to copper. In addition, Aleksandar Durman, in his 1997 paper "Tin in South-eastern Europe?", essentially initiated studies into the role of the Balkans in Europe's Bronze Age tin economy. He identified six geologically favourable sites for tin mineralisation and associated fluvial placer deposits in the former Yugoslavian republics, and suggested that these may have added to the tin supply of the region. The viability of two of these sites has been confirmed (Mt Cer and Bukulja, Serbia) but the exploitation potential for the other locations has remained untested. River gravels from these four sites (Motajica and Prosara in Bosnia and Herzegovina; Bujanovac in Serbia; Ogražden in North Macedonia) were obtained by stream sluicing and panning. The sites of Prosara and Bujanovac were found to be barren with respect to cassiterite (SnO 2). Streams flowing from Motajica and Ogražden were both found to contain cassiterite, but in amounts several orders of magnitude less than at Mt Cer and Bukulja. Although it is possible that minor tin recovery occurred at Motajica and Ogražden, it is unlikely that they could have contributed meaningfully to regional tin trade. This is supported by the fact that the isotopic signature (d 124 Sn) of cassiterite from Motajica is highly enriched in light isotopes of tin compared to that associated with Late Bronze Age artefacts of the region

The Giant Chalukou Porphyry Mo Deposit, Northeast China: The Product of a Short-Lived, High Flux Mineralizing Event

Whether giant porphyry ore deposits are the products of single, short-lived magmatic-hydrothermal events or multiple events over a prolonged interval is a topic of considerable debate. Previous studies, however, have all been devoted to porphyry Cu and Cu-Mo deposits. In this paper, we report high-precision isotope dilution-negative-thermal ionization mass spectrometric (ID-N-TIMS) molybdenite Re-Os ages for the newly discovered, world-class Chalukou porphyry Mo deposit (reserves of 2.46 Mt @ 0.087 wt % Mo) in NE China. Samples were selected based on a careful evaluation of the relative timing of the different vein types (i.e., A, B, and D veins), thereby ensuring that the suite of samples analyzed could be used to reliably determine the age and duration of mineralization. The molybdenite Re-Os geochronology reveals that hydrothermal activity at Chalukou involved two magmatic-hydrothermal events spanning an interval of 6.92 ± 0.16 m.y. The first event (153.96 ± 0.08/0.63/0.79 Ma, molybdenite ID-N-TIMS Re-Os age) was associated with the emplacement of a granite porphyry dated at 152.1 ± 2.2 Ma (zircon laser ablation-inductively coupled plasma-microscopic [LA-ICP-MS] U-Pb ages), and led to only minor Mo mineralization, accounting for 90%) was deposited in less than 650 kyr, between 147.67 ± 0.10/0.60/0.76 and 147.04 ± 0.12/0.72/0.86 Ma (molybdenite ID-N-TIMS Re-Os ages), coincident with the emplacement of a fine-grained porphyry at 148.1 ± 2.6 Ma (zircon LA-ICP-MS U-Pb ages). The high-precision Re-Os age determinations presented here show, contrary to the finding of a number of studies of porphyry Cu and Cu-Mo systems, that the giant Chalukou porphyry Mo deposit primarily formed in a single, short-lived (<650 kyr) hydrothermal event, suggesting that this may also have been the case for other giant porphyry Mo deposits

The Shepherd Mountain Iron Ore Deposit in Southeast Missouri, USA – an Extension of the Pilot Knob Magmatic-Hydrothermal Ore System: Evidence from Iron Oxide Chemistry

The Southeast Missouri Iron Metallogenic Province in the Midcontinent USA contains seven major and several minor IOA/IOCG-type deposits and a series of shallow vein-type deposits/prospects, all of which are spatially and temporally associated with early Mesoproterozoic (1500–1440 Ma) magmatism in the St. Francois Mountains terrane. One of the vein-type deposits is the Shepherd Mountain deposit, which consists of two northeast-trending ore veins dominated by magnetite and lesser amounts of hematite. Here we report the findings of a study that investigates the origin of the Shepherd Mountain deposit and a possible genetic link to the nearby (i.e., away) magmatic to magmatic-hydrothermal Pilot Knob ore system that comprises the massive-to-disseminated Pilot Knob Magnetite deposit and the overlying bedded and brecciated Pilot Knob Hematite deposit. Petrographic observations, whole-rock data and the trace element and Fe isotope composition of magnetite and hematite show that the Shepherd Mountain deposit formed from at least five pulses of magmatic-hydrothermal fluids with different compositions and physicochemical parameters. Integration of the data for the Shepherd Mountain deposit with new and published data from the Pilot Knob Magnetite and Pilot Knob Hematite deposits shows that the three deposits are genetically linked through two local faults. The Ironton and Pilot Knob faults provided fluid pathways that connected the Pilot Knob Magnetite deposit to the shallower Shepherd Mountain and Pilot Knob Hematite deposits. Consequently, we argue that the Shepherd Mountain and Pilot Knob Hematite deposits are near-surface extensions of the same magmatic to hydrothermal plumbing system that formed the Pilot Knob Magnetite deposit at depth

The Fe-Zn Isotopic Characteristics and Fractionation Models: Implications for the Genesis of the Zhaxikang Sb-Pb-Zn-Ag Deposit in Southern Tibet

The genesis of the Zhaxikang Sb-Pb-Zn-Ag deposit remains controversial. Three different geological environments have been proposed to model mineralization: a hot spring, a magmatic-hydrothermal fluid, and a sedimentary exhalative (SEDEX) overprinted by a hot spring. Here, we present the electron probe microanalysis (EPMA) and Fe-Zn isotopic data (microsampled) of four samples from the first pulse of mineralization that show annular textures to constrain ore genesis. The Zn/Cd ratios from the EPMA data of sphalerite range from 296 to 399 and overlap the range of exhalative systems. The δ56Fe values of Mn-Fe carbonate and δ66Zn values of sphalerite gradually decrease from early to late stages in three samples. A combination of the EPMA and isotopic data shows the Fe-Zn contents also have different correlations with δ66Zn values in sphalerite from these samples. Rayleigh distillation models this isotope and concentration data with the cause of fractionation related to vapour-liquid partitioning and mineral precipitation. In order to verify this Rayleigh distillation model, we combine our Fe-Zn isotopic data with those from previous studies to establish 12 Fe-Zn isotopic fractionation models. These fractionation models indicate the δ56Fei and δ66Zni values (initial Fe-Zn isotopic compositions) of the ore-forming system are in the range of -0.5‰​​ ~−1‰ and -0.28‰​ ~0‰, respectively. To conclude, the EPMA data, Fe-Zn isotopic characteristics, and fractionation models support the SEDEX model for the first pulse of mineralization

Genesis Of The 1.45 Ga Kratz Spring Iron Oxide-Apatite Deposit Complex In Southeast Missouri, USA: Constraints From Oxide Mineral Chemistry

Seven major and numerous lesser Fe oxide occurrences within the 1.47 Ga St. Francois Mountains terrane in Missouri (USA) have previously been described as iron oxide-apatite (IOA) and iron oxide-copper-gold (IOCG) deposits. Researchers speculate that these contain significant amounts of critical minerals, most notably rare earth elements and cobalt. One of the less-studied deposits in the region is the 1.455 Ga Kratz Spring deposit. The deposit consists of two steeply dipping magnetite bodies beneath 450 m of sedimentary cover. The genesis of the Kratz Spring deposit and its relationship to nearby IOA-IOCG deposits remains poorly constrained. To better understand the formation of the Kratz Spring deposit, the authors integrated stratigraphic, petrographic, and bulk rock studies within situ trace element and Fe isotope chemistry of magnetite and hematite. These data show that the Kratz Spring deposit is hydrothermal in origin but is divided into two sub deposits according to different fluid sources and formation conditions: (1) a deep but cooler hydrothermal Kratz Spring South deposit with a juvenile fluid source and (2) a shallow but hotter magmatic-hydrothermal Kratz Spring North deposit with variable fluid sources. Our genetic model suggests the two Kratz Spring deposits are local expressions of the same mineralization system, i.e., the Kratz Spring South deposit is a distal, lower-temperature offshoot of the feeder system that formed the Kratz Spring North deposit. Understanding the magmatic-hydrothermal plumbing system that formed Missouri\u27s IOA-IOCG deposits is important to guiding critical mineral exploration efforts in the region

First results from 2+1 dynamical quark flavors on an anisotropic lattice: light-hadron spectroscopy and setting the strange-quark mass

We present the first light-hadron spectroscopy on a set of $N_f=2+1$ dynamical, anisotropic lattices. A convenient set of coordinates that parameterize the two-dimensional plane of light and strange-quark masses is introduced. These coordinates are used to extrapolate data obtained at the simulated values of the quark masses to the physical light and strange-quark point. A measurement of the Sommer scale on these ensembles is made, and the performance of the hybrid Monte Carlo algorithm used for generating the ensembles is estimated.Comment: 24 pages. Hadron Spectrum Collaboratio

A 4 Gyr M-dwarf Gyrochrone from CFHT/MegaPrime Monitoring of the Open Cluster M67

We present stellar rotation periods for late K- and early M-dwarf members of the 4 Gyr old open cluster M67 as calibrators for gyrochronology and tests of stellar spin-down models. Using Gaia EDR3 astrometry for cluster membership and Pan-STARRS (PS1) photometry for binary identification, we build this set of rotation periods from a campaign of monitoring M67 with the Canada-France-Hawaii Telescope's MegaPrime wide field imager. We identify 1807 members of M67, of which 294 are candidate single members with significant rotation period detections. Moreover, we fit a polynomial to the period versus color-derived effective temperature sequence observed in our data. We find that the rotation of very cool dwarfs can be explained by a simple solid-body spin-down between 2.7 and 4 Gyr. We compare this rotational sequence to the predictions of gyrochronological models and find that the best match is Skumanich-like spin-down, P_rot \propto t^0.62, applied to the sequence of Ruprecht 147. This suggests that, for spectral types K7-M0 with near-solar metallicity, once a star resumes spinning down, a simple Skumanich-like is sufficient to describe their rotation evolution, at least through the age of M67. Additionally, for stars in the range M1-M3, our data show that spin-down must have resumed prior to the age of M67, in conflict with predictions of the latest spin-down models.Comment: 21 pages, 16 figures, Accepted for publication by Ap