Kevin Faure

Fluid chemistry of Archean seafloor hydrothermal vents: Implications for the composition of circa 3.2 Ga seawater

Seafloor hydrothermal vents of mid-Archean age (ca. 3230 Ma) have been identified and mapped in the Barberton greenstone belt, South Africa and are known as the Ironstone Pods. Fluid inclusion homogenization temperature data, when combined with gas chromatographic data, provide a minimum calculated water depth for the pods of 982 m. Ironstone Pod hydrothermal fluid endmember concentrations (Mg = 0) of various dissolved components derived from bulk fluid inclusion crush-leach experiments, include: Cl(730 mmol/L), Br (2.59), I (0.058), Na (822), NH4 (11.4), K (21.5), Ca (42.6), and Sr (0.15). This hydrothermal fluid also contains up to 1.07 mol% CO2, 0.03 mol% N2, 0.02 mol% CH4, 262 ppm COS, and minor amounts of C2–C4 hydrocarbons. Hydrothermal endmember Ca, Sr, and NH4, in particular, and to a lesser degree K, I, and CO2, commonly plot on, or very close to, modern vent fluid trends. By contrast, endmember Na and Br concentrations are distinct (higher) from modern vent fluids. High I and NH4 concentrations are consistent with contributions from sediments and/or organic matter. Calculated δ18OH2O values for the pod hydrothermal endmember fluid define a narrow range from 0.9 to 1.6‰ very similar to that of modern vent fluid values (0.4–2.1‰). A best estimate for the Ironstone Pod seawater endmember composition is Cl (920 mmol/L), Br (2.25), SO4 (2.3), I (0.037), Na (789), NH4 (5.1), K (18.9), Mg (50.9), Ca (232), and Sr (4.52). Barberton seawater components are commonly within an order of magnitude of modern seawater values, with the exception of significantly higher 1, NH4, Ca, and Sr in the inclusions. Sulfate concentrations are minimum estimates for Barberton seawater. Fluid inclusion samples containing the greatest amount of seawater component have higher N2 (up to 0.1 mol%) and low CO2, when compared to samples dominated by the hydrothermal endmember fluid. Barberton ambient seawater is considered to have been an evaporative brine of NaClCaCl2 composition during the time of pod deposition. Ironstone Pod fluid inclusion seawater endmember Br/Cl and I/Cl values of 2.45 × 10−3 and 40.2 × 10−6, respectively, are within error of bulk Earth (2.38 × 10−3 and 190 × 10−6) and are consistent with the chemistry of 3.23 Ga Barberton seawater being buffered by the mantle.

Poor quality vital anti-malarials in Africa - an urgent neglected public health priority

BackgroundPlasmodium falciparum malaria remains a major public health problem. A vital component of malaria control rests on the availability of good quality artemisinin-derivative based combination therapy (ACT) at the correct dose. However, there are increasing reports of poor quality anti-malarials in Africa.MethodsSeven collections of artemisinin derivative monotherapies, ACT and halofantrine anti-malarials of suspicious quality were collected in 2002/10 in eleven African countries and in Asia en route to Africa. Packaging, chemical composition (high performance liquid chromatography, direct ionization mass spectrometry, X-ray diffractometry, stable isotope analysis) and botanical investigations were performed.ResultsCounterfeit artesunate containing chloroquine, counterfeit dihydroartemisinin (DHA) containing paracetamol (acetaminophen), counterfeit DHA-piperaquine containing sildenafil, counterfeit artemether-lumefantrine containing pyrimethamine, counterfeit halofantrine containing artemisinin, and substandard/counterfeit or degraded artesunate and artesunate+amodiaquine in eight countries are described. Pollen analysis was consistent with manufacture of counterfeits in eastern Asia. These data do not allow estimation of the frequency of poor quality anti-malarials in Africa.ConclusionsCriminals are producing diverse harmful anti-malarial counterfeits with important public health consequences. The presence of artesunate monotherapy, substandard and/or degraded and counterfeit medicines containing sub-therapeutic amounts of unexpected anti-malarials will engender drug resistance. With the threatening spread of artemisinin resistance to Africa, much greater investment is required to ensure the quality of ACTs and removal of artemisinin monotherapies. The International Health Regulations may need to be invoked to counter these serious public health problems.

U-Pb geochronology of mid-Paleozoic plutonism in western New Zealand: Implications for S-type granite generation and growth of the east Gondwana margin

New U-Pb isotope-dilution-thermal ionization mass spectrometry (ID-TIMS) ages (371–305 Ma) for 30 granitic plutons along the New Zealand sector of the East Gondwanan active margin reveal a highly episodic emplacement history and crustal growth pattern. The Late Devonian-late Carboniferous ages also establish specific links with both the mostly older, Lachlan and the mostly younger, New England fold belts of eastern Australia. Dated plutons are representative of two S- and I-type suite pairs, the volumetrically predominant Karamea-Paringa (371–360 Ma) and minor Ridge-Tobin (355–342 Ma) pulses, as well as sporadic Foulwind Suite A-type granites (350–305 Ma). Emplacement of the bulk of the dominant ∼3400 km 2 Karamea Suite S-type granite-granodiorite plutons within a 2.11 Ma interval is explained by major and intimate intrusion of mantle-derived magma into largely metasedimentary crust during intra-arc extension of previously overthickened crust. Transient emplacement rates were thus of similar magnitude as some young ignimbrite flare-ups and an order of magnitude greater than long-term averages for Mesozoic-Cenozoic cordilleran batholiths of the western Americas. Extension likely was terminated abruptly by resumption of convergence, possibly associated with amalgamation of the Buller and Takaka terranes, between 368 and 355 Ma. Significant crustal growth occurred during generation of the two S-type suites, where mantle basalt contributed mass, and heat for rapid melting, during transient intra- or backarc extensional episodes. In contrast, the I-type suites were dominated by partial melting of meta-igneous crust, and they are relatively small in volume. The Karamea S-type suite shares striking similarities in terms of age, composition, and extensional tectonic setting with S-type granites of the Melbourne terrane of the Lachlan fold belt. Both regions may have formed in a backarc position with respect to the Late Devonian-early Carboniferous subduction zone in the New England fold belt. Foulwind Suite A-type magmatism in New Zealand overlaps in age with the widespread 320–285 Ma A- and I-type magmatism in the northern New England fold belt. The likely continuation of the New England subduction system must have subsequently been removed from outboard of the New Zealand region after 320–285 Ma magmatism, and prior to Triassic accretion of a Permian oceanic arc terrane to the New Zealand margin.

Discovery of hydrothermal sulfide mineralization from southern Kermadec arc volcanoes (SW Pacific)

Abstract We report the discovery of hydrothermal sulfide mineralization within the summit caldera of two southern Kermadec frontal arc volcanoes (Brothers and Rumble II West) of the ∼1200 km long, Kermadec–Havre arc–back-arc system. The Brothers and Rumble II (West) calderas, both with re-surgent domes and comprising mostly dacite and basalt–andesite host rocks, respectively, rise to water depths of ≤1500 m. These calderas comprise mostly effusive lavas and volcaniclastic deposits, including talus breccias along their inner caldera walls. These two southern Kermadec hydrothermal sites have similar geological settings and mineralogy to other arc front vent sites. Two principle ore assemblages are identified, comprising: (i) chalcopyrite–pyrite–barite, and (ii) sphalerite–marcasite–barite ± pyrite. The most prevalent ore texture consists of massive chalcopyrite + pyrite ± sphalerite, commonly overprinting barite. Early marcasite cores within large, euhedral pyrites, and trails of pyrite inclusions within chalcopyrite are indicative of recrystallization. The ore mineralogy is consistent with postulated venting temperatures of ≥300°C. Sulfide geochemistry is consistent with the ore mineralogy with concentrations of Cu, Fe, and Zn up to 15.3, 19.1, and 18.8 wt%, respectively. The sulfide geochemistry is distinct, however, from comparable western Pacific vent sites, and may reflect source heterogeneity due to proximity to continental New Zealand and sediment recycling along the southern Kermadec trench–arc system. The recovery of two partial caridean vent shrimps suggests that present-day hydrothermal venting is occurring within the Brothers caldera.

Methane seepage and its relation to slumping and gas hydrate at the Hikurangi margin, New Zealand

Abstract Dissolved methane and high resolution bathymetry surveys were conducted over the Rock Garden region of Ritchie Ridge, along the Hikurangi margin, eastern New Zealand. Multibeam bathymetry reveals two prominent, northeast trending ridges, parallel to subduction along the margin, that are steep sided and extensively slumped. Elevated concentrations of methane (up to 10 nM, 10× background) within the water column are associated with a slump structure at the southern end of Eastern Rock Garden. The anomalous methane concentrations were detected by a methane sensor (METS) attached to a conductivity‐temperature‐depth‐optical backscatter device (CTDO) and are associated with elevated light scattering and flare‐shaped backscatter signals revealed by the ships echo sounder. Increased particulate matter in the water column, possibly related to the seepage and/or higher rates of erosion near slump structures, is considered to be the cause of the increased light scattering, rather than bubbles in the water column. Methane concentrations calculated from the METS are in good agreement with concentrations measured by gas chromatography in water samples collected at the same time. However, there is a c. 20 min (c. 900 m) delay in the METS signal reaching maximum CH4 concentrations. The maximum methane concentration occurs near the plateau of Eastern Rock Garden close to the edge of a slump, at 610 m below sea level (mbsl). This is close to the depth (c. 630 mbsl) where a bottom simulating reflector (BSR) pinches out at the seafloor. Fluctuating water temperatures observed in previous studies indicate that the stability zone for pure methane hydrate in the ocean varies between 630 and 710 mbsl. However, based on calculations of the geothermal gradients from BSRs, we suggest gas hydrate in the study area to be more stable than hydrate from pure methane in sea water, moving the phase boundary in the ocean upward. Small fractions of additional higher order hydrocarbon gases are the most likely cause for increased hydrate stability. Relatively high methane concentrations have been measured down to c. 1000 mbsl, most likely in response to sediment slumping caused by gas hydrate destabilisation of the sediments and/or marking seepage through the gas hydrate zone.

Fluid chemistry of veining associated with an ancient microearthquake swarm, Benmore Dam, New Zealand

Steeply dipping strata in the vicinity of Benmore Dam, Otago, New Zealand, are complexly deformed metasedimentary rocks of the Torlesse Supergroup (Middle Triassic age). Over an exposed area ∼100 m wide × 25 m high, these strata are disrupted by a fault-fracture mesh comprising conjugate Coulomb shears interlinked by extensional and extensional-shear fractures, all formed in a common stress field and hosting quartz + prehnite ± epidote ± calcite veining. The combined effect of these structures is shortening perpendicular to beddings and subvertical extension so that in their present attitude, they correspond to a set of conjugate thrust faults with associated extension fractures. On the evidence of incremental vein textures, the development of this distributed fault-fracture mesh is interpreted as resulting from a fluid-driven microearthquake swarm, which postdated regional low-grade metamorphism. Mechanical considerations suggest that the migrating hydrothermal fluids were significantly overpressured, possibly to approximately lithostatic values, if the mesh structure developed in its present attitude. Fluid-inclusion microthermometric studies show that Benmore vein quartz contains two-phase aqueous inclusions with salinities between 1.4 and 2.9 wt% NaCl equivalent and homogenization temperatures ( T h ) between 189 and 217 °C. The assemblage quartz + prehnite + epidote suggests trapping temperatures ( T t ) of ∼280 °C, requiring the addition of an ∼70 °C correction to T h values. Late calcite contains inclusions with noticeably lower salinity (0.0–0.9 wt% NaCl) and T h values (129–175 °C). Studies on quartz + pumpellyite ± calcite veins from nearby Lake Aviemore show similar fluid-inclusion salinity and T h values. Fluid-inclusion gas analyses show all the vein samples to be dominated by H 2 O (99.3–99.9 mol%) with few other gases apparent, including CH 4 (≤0.5%), N 2 (≤0.1%), CO 2 (≤0.1%), and C 2 -C 4 hydrocarbons. Cation and anion analyses, when combined with the gas data, show that NaCl dominates the fluid-inclusion salinities. Oxygen isotope results, when combined with calculated T t values, indicate that the water responsible for the deposition of Benmore and Aviemore quartz had δ 18 O compositions of 9.4‰ and 4.8‰, respectively. Calcite δ 13 C values between−25.3‰ and−38.0‰ are indicative of oxidation of CH 4 to CO 2 as a result of hydrothermal fluids interacting with organic- rich sediments. Fluid-inclusion \({\delta}D_{H_{2}O}\) values for Benmore range between −73‰ and −89‰ compared to−109‰ for the one Aviemore sample. This research has demonstrated that (1) water of meteoric origin, probably from subantarctic latitudes, penetrated to ≥6 km depth and underwent an oxygen isotope shift before depositing the Benmore-Aviemore veins; (2) the migrating hydrothermal fluids were likely overpressured well above hydrostatic to near lithostatic values if the mesh structure was active in its present orientation; and, (3) fluid migration was coupled to distributed brittle failure in the prevailing stress field, “self-generating” a permeable fault-fracture mesh.

Geology, mineralogy and geochemistry of the rhyolite-hosted Maungaparerua clay deposit, Northland

A rhyolite dome complex at Maungaparerua, Ar/Ar dated at 3.7 ± 0.04 Ma (Early Pliocene), is bounded on the west by a sequence of hydrothermally altered basalt flows intercalated with several non-marine siltstone and rhyolitic tuff units. This basalt sequence and the rhyolite dome complex are overlain by younger unaltered basalt flows. Within the dome complex, several small pits have been worked in the past for china clays. Recent drilling has outlined a halloysite-rich ‘Southern Area’ extending to a depth of up to 24 m below the present-day erosion surface. Primary sanidine and plagioclase phenocrysts are completely leached in halloysite-rich rhyolite, but are only partially leached at greater depth. Halloysite-rich rhyolite is characterised by relative enrichment in loss on ignition (LOI; 5–9%) and Al2O3 (18–24%) and depletion in K2O (<0.5%), compared with 2.0% LOI, 15.0% Al2O3 and 4.1% K2O in least-altered rhyolite. Oxygen and hydrogen isotope compositions of halloysite samples indicate that it is of supergene rather than hydrothermal origin. This is consistent with weathering type clay profiles in halloysite-rich zones. Although there is earlier hydrothermal alteration in the form of silicified rhyolite 800 m to the west of the Southern Area and kaolinite-pyrite alteration in the adjacent basalt, we conclude that the dominant process in the formation of the halloysite was deep weathering of sanidine rhyolite under water-saturated subtropical conditions.

Pyrite-coated granite cobbles at Lee Bay, Stewart Island

On the west side of Lee Bay on the northeast coast of Stewart Island, ventifact cobbles of pyrite-coated granite occur on the beach near the high tide mark and appear to be derived from a sand-cemented gravel deposit that forms a low bank at the back of the beach. The pyrite coat (up to 1 mm thick) completely covers the granitic cobbles and is zoned, with an inner zone of fine-grained colloform pyrite and an outer framboidal zone. Framboidal pyrite is typically formed in anoxic sedimentary environments. Subrounded grains of hematite, ilmenite with hematite blebs, magnetite, feldspar, biotite, quartz and zircon are present in the outer framboidal zone, with some ilmenite and hematite grains being partially replaced by pyrite. The assemblage of ilmenite-hematite-magnetite-biotite-zircon is similar both in mineralogy and size range to that found in heavy mineral beach sands. Sulphur isotope values of the pyrite coat are consistent with formation of the pyrite by microbial sulphate reduction of seawater sulphate. The framboidal texture together with the presence of grains of beach sand in the pyrite coating indicate that it was deposited in a low-temperature sedimentary environment.

Gold mineralisation in the polymetallic Sams Creek peralkaline microgranite, South Island, New Zealand

Abstract At Sams Creek, a peralkaline microgranite dyke intrudes Lower Palaeozoic greenschist facies metasediments. The granitedyke has been extensively silicified and hosts stockwork veins composed of quartz, siderite, and arsenopyrite + pyrite ± gold ± galena ± sphalerite ± chalcopyrite ± pyrrhotite. Alteration and gold mineralisation are confined to the granite, and these features together with the style of veining and the sulphide mineralogy indicate that mineralisation is related to granite rather than to an external metamorphic source. Calculated δ18OH2O values from vein quartz and siderite range between 6 ℵ and 9 ℵ, and between 6 ℵ and 8 ℵ (VSMOW), respectively. δ13C values of siderite are all about − 5 ℵ (VPDB) and δ34S values of the sulphides have a narrow range with an average of +9.0ℵ (CDT). These oxygen, carbon, and sulphur isotope values of the vein minerals (quartz, siderite, and sulphides) are consistent with a magmatic-hydrothermal fluid source, but they could also be derived from a metamorphic source.