Cl Enrichment Research Articles

Chlorine-Enriched Tourmalines In Hydrothermally Altered Diorite Porphyry From the Biely Vrch Porphyry Gold Deposit (Slovakia)

Chlorine-enriched tourmaline was found in a hydrothermally altered Miocene diorite porphyry at the Biely Vrch porphyry gold deposit (Central Slovakia) as a relatively rare alteration mineral forming radial aggregates composed of thin prismatic crystals in the central part of quartz veinlets filled by calcite. Zoned tourmaline with Cl-enriched central zones is accompanied by allanite-(Ce) to epidote, fluorapatite, Al-rich titanite, magnetite, rutile, ilmenite, and pyrite. The tourmaline chemical composition is controlled by exchange of Fe 2+ for Al at relatively constant Mg content. It produces a trend from the earliest X -site vacant Al-rich oxy-tourmaline in the central part of tourmaline aggregates to the latest feruvite on their margins. Tourmalines belong to three groups: X -site vacant (“ vacancy-Mg-O root name” tourmaline, magnesio-foitite, and foitite), alkali (oxy-schorl, schorl), and calcic (feruvite) tourmaline. The variation in Al and Fe content is the result of concomitant action of AlOFe −1 OH) −1 , Al X □Fe −1 Na −1 , and FeCaAl −1 Na −1 substitutions. Enrichment in Ca likely results from FeCaAl −1 Na −1 substitution. The Cl content in tourmaline from Biely Vrch attains 0.45 wt.%, which is equivalent to 0.126 apfu . The chlorine content increases with decreased Fe and increased octahedral Al and X -site vacancy. Bond-length calculations yield six bond-valence and bond-length probable local structural arrangements with W Cl, and these are all characterized by dominance of Al at the Y sites and O at the V sites. Based on the analytical data and bond-length calculations, the chemical composition of Cl-enriched tourmaline is a result of crystallographic factors as well as petrologic environmental conditions. The enrichment in Cl is most likely related to the unusually Cl-rich hot hydrothermal fluid responsible for the origin of the host Biely Vrch porphyry gold deposit. The Cl incorporation in tourmaline is influenced by Fe availability in the genetic environment; increased Fe 2+ substitution for Al reduces the ability of tourmaline to incorporate Cl.

Chlorine isotopes of thermal springs in arc volcanoes for tracing shallow magmatic activity

The evaluation of the status of shallow magma body (i.e., from the final intrusion stage, to quiescence, and back to activity), one of the key parameters that trigger and sustain volcanic eruptions, has been challenging in modern volcanology. Among volatile tracers, chlorine (Cl) uniquely exsolves at shallow depths and is highly hydrophilic. Consequently, Cl enrichment in volcanic gases and thermal springs has been proposed as a sign for shallow magmatic activities. However, such enrichment could also result from numerous other processes (e.g., water evaporation, dissolution of old chloride mineral deposits, seawater contamination) that are unrelated to magmatic activity. Here, based on stable isotope compositions of chloride and dissolved inorganic carbon, as well as previous published 3He/4He data obtained in thermal springs from two recently erupted volcanoes (La Soufrière in Guadeloupe and Montagne Pelée in Martinique) in the Lesser Antilles Arc, we show that the magmatic Cl efficiently trapped in thermal springs displays negative δ37Cl values (≤−0.65‰), consistent with a slab-derived origin but distinct from the isotope compositions of chloride in surface reservoirs (e.g. seawater, local meteoric waters, rivers and cold springs) displaying common δ37Cl values of around 0‰. Using this δ37Cl difference as an index of magmatic Cl, we further examined thermal spring samples including a 30-year archive from two thermal springs in Guadeloupe covering samples from its last eruption in 1976–1977 to 2008 and an island-wide sampling event in Martinique in 2008 to trace the evolution of magmatic Cl in the volcanic hydrothermal systems over time. The results show that magmatic Cl can be rapidly flushed out of the hydrothermal systems within <30 to 80 years after the eruption, much quicker than other volatile tracers such as CO2 and noble gases, which can exsolve at greater depths and constantly migrate to the surface. Because arc volcanoes often have well developed hydrothermal systems where magmatic Cl is easily transferred to the surface following its exsolution from shallow magma body, we suggest that δ37Cl has great potential to be a unique proxy to monitor the cessation and revival of infrequent arc volcanoes, particularly at centennial time scales.

Interaction of Biotite–Amphibole Gneiss with H2O–CO2–(K, Na)Cl Fluids at 550 MPa and 750 and 800°С: Experimental Study and Applications to Dehydration and Partial Melting in the Middle Crust

To constrain effects of chloride-bearing H2O^CO2 fluids on complex natural assemblages during high-grade metamorphism and anatexis, we report the results of experiments on the interaction of biotite^ hornblende tonalitic gneiss from the Sand River Formation (Limpopo Complex, South Africa) with H2O^CO2, H2O^CO2^ KCl, H2O^CO2^NaCl, and H2O^CO2^(K, Na)Cl fluids at 550MPa, 750 and 8008C, and varying chloride/(H2OþCO2) ratios with molar CO2/(CO2þH2O)1⁄4 0 5. Heating of solid cylinders of gneiss at both temperatures in the absence of a free fluid phase produced no changes in the gneiss phase assemblage.The equimolar H2O^CO2 fluid at 7508Q also did not significantly influence the phase assemblage. Addition of KCl to the fluid at 7508Q resulted in formation of the clinopyroxeneþK-feldspar (þ ilmenite/titanite) assemblage after biotite, hornblende and plagioclase. Orthopyroxene accompanied by amphibole appeared only at 8008C as a result of biotite breakdown in the presence of H2O^CO2 and low-salinity H2O^CO2^KCl fluids. Increase in the KCl content in the fluid at 8008Q resulted in the production of a clinopyroxenebearing assemblage. Increase of the NaCl content stabilized amphibole in an assemblage with either orthopyroxene (at low NaCl concentrations) or clinopyroxene. Nevertheless, clinopyroxene (þ albite) is stable only at high salt concentrations. Comparison of the experimental results with the results of thermodynamic modeling using the Gibbs free energy minimization method (PERPLE_X software) showed that mineral reactions and assemblages in the run products were governed by the activities of alkali components imposed by KCl and NaCl in the H2O^CO2 fluids, and decrease of the water activity served as an additional factor stabilizing anhydrous assemblages. No melts formed at 7508C in the presence of the H2O^CO2^KCl fluids. These fluids provoked melting only at 8008C with formation of rhyolitic melts.With increasing KCl content of the fluid, the melt composition changed to potassic rhyolitic with Al2O3513 5 wt %, CaO52 wt %, K2OþNa2O47 wt %, FeO/(FeOþMgO)40 8, K2O/Na2O41, and moderate enrichment in Cl (0 2^0 6 wt %). Increasing NaCl content caused melting at 7508Q and shifted the melt composition towards trachytic and trachyandesitic compositions at both 750 and 8008Q. The experiments support a model for the formation of ferroan A-type granite^syenite complexes via crustal melting in the presence of H2O^CO2^salt fluids in extensional tectonic settings.They demonstrate a possible link between A-type granitoids and mid-crustal dehydration zones in amphiboliteto granulite-facies terrains and allow a new interpretation of mineral assemblages within these zones in terms of variations in fluid salinity.

The Lac Des Iles Palladium Deposit, Ontario, Canada. Part II. Halogen variations in apatite

Analysis of apatite from the Mine Block Intrusion (MBI) of the Lac des Iles Igneous Complex shows two pronounced trends in the halogens. Apatite from relatively fresh norite and melanorites from the Pd-sulfide zone contain up to 57 mol% chlorapatite endmember with significant hydroxyapatite component. In contrast, in altered rock (amphibolite and greenschist assemblages) the chlorapatite component is typically less than 10 mol% with wide variation in the F- and OH-endmember components. The latter trend is attributed to Cl loss to degassing and alteration, whereas the former is attributed to Cl enrichment in the ore-bearing rocks. It is suggested that the relatively H2O-rich and intermediate Cl content of the early igneous fluids degassed from the deeper levels of the MBI can explain the high Pd/Pt and Pd/Ir ratios of the deposit. A model is presented in which disseminated Pd-rich sulfides are initially introduced by a high-temperature magmatic fluid that also influenced crystallization to produce the gross modal variations of the igneous host rock. This high-temperature mineralization event was subsequently modified by the influx of late igneous and country fluids at amphibolite to greenschist conditions.

Alteration assemblages in the Miller Range and Elephant Moraine regions of Antarctica: Comparisons between terrestrial igneous rocks and Martian meteorites

AbstractThe weathering products present in igneous terrestrial Antarctic samples were analyzed, and compared with those found in the four Miller Range nakhlite Martian meteorites. The aim of these comparisons was to determine which of the alteration phases in the Miller Range nakhlites are produced by terrestrial weathering, and what effect rock composition has on these phases. Antarctic terrestrial samples MIL 05031 and EET 96400, along with the Miller Range nakhlites MIL 03346 and 090032, were found to contain secondary alteration assemblages at their externally exposed surfaces. Despite the difference in primary mineralogy, the assemblages of these rocks consist mostly of sulfates (jarosite in MIL 05031, jarosite and gypsum in EET 96400) and iddingsite‐like Fe‐clay. As neither of the terrestrial samples contains sulfur‐bearing primary minerals, and these minerals are rare in the Miller Range nakhlites, it appears that SO42−, possibly along with some of the Na+, K+, and Ca+ in these phases, was sourced from wind‐blown sea spray and biogenic emissions from the southern ocean. Cl enrichment in the terrestrially derived “iddingsite” of MIL 05031 and MIL 03346, and the presence of halite at the exterior edge of MIL 090032, can also be explained by this process. However, jarosite within and around the olivine‐bound melt inclusions of MIL 090136 is present in the interior of the meteorite and, therefore, is probably the product of preterrestrial weathering on Mars.

Water pollution in relation to mineral exploration: a case study from Alayi-Ovim area of Southeastern Nigeria

Water samples from rivers, streams, springs, and shallow wells in Alayi-Ovim area of southeast Nigeria have been analyzed for Pb, Ca, Mg, Fe, Mg, PO(4), NO(3), CO(3), SO(4), Cl, and pH. The analyses were carried out using atomic absorption spectrometer and Hach Direct Reading Equipment. Results of the analyses from the area conform to the WHO (1995) standards for drinking water. However, the results show relative enrichment of Ca, pH, Mg, CO(3), and Cl. Low values were obtained for Fe, SO(4), and NO(3). While the Cl and Pb enrichment in the area north of Alayi-Ovim axis is attributed to proximity to the lead-zinc and chloride-rich formations of the Turonian Eze-Aku and the Albian Asu River; the Ca, Mg, SO(4), and CO(3) enrichment in Southern part of Alayi-Ovim is due to the limestone-bearing Late Maastrichtian Nsukka Formation. Furthermore, the very low values of less than 5ppm for these characters in water in the central region correlate well with the relatively clean Maastrichtian quartz arenite Ajali Sandstone Formation. The Pb-Zn and Cl incursions into the water system from the Older Albian Asu River/Turonian Eze-Aku Formations in the northern part of Alayi-Ovim area and the leaching of Mg, and Ca into the water system in the Maastrichtian limestone area in the south thus constitute geochemical indices for chemical pollution and mineral exploration for brine and dolomitic limestone in the area.

Insights into the origin of primitive silica-undersaturated arc magmas of Aoba volcano (Vanuatu arc)

Aoba picrites in Vanuatu arc (Southwestern Pacific) offer the opportunity to address the question of the origin of Si-undersaturated arc magmas, through the geochemical study of their olivine-hosted melt inclusions. These latter delineate a differentiation trend of calc-alkaline silica-undersaturated basalts, with typical trace-element patterns of arc magmas. The most primitive melt inclusions, preserved in olivines with Fo ≥ 89, have normative nepheline compositions with CaO/Al2O3 > 0.8, but belong to three distinct populations differing in their enrichment or depletion in LILE, Cl, and alkalis (Rb, K). The dominant population is characterized by medium-LILE concentrations (La/Yb ~ 7–8) and represents the parental magma of the Aoba lavas. The two others (La/Yb ~ 20 and 2) are either significantly enriched or extremely depleted in LILE, Cl, and alkalis. This compositional variability of primitive magma batches requires the multi-stage mixing between melts generated by partial melting of both peridotite and clinopyroxene-rich lithologies. Medium-LILE magma derives from the mixing between peridotite- and clinopyroxenite-derived melts, whereas the high- and low-LILE melts involve amphibole-bearing and amphibole-free clinopyroxenite sources, respectively.

Major and trace element partition and fluxes in the Rhône River

Dissolved and particulate major and trace element concentrations and suspended particulate contents were determined during three years on the lower Rhône River (France) from subsurface water samples collected about twice a month and more regularly during flood events. Dissolved elements can be grouped into two sets showing similar relationship between concentration and water discharge related to dilution process and to local and diffuse inputs of dissolved elements in the Rhône basin. The variation of NO 3/Na and Cl/Na ratios and the absence of correlation between NO 3 and the enrichment in Cl show that Rhône River is not highly affected by fertilizer applications compared to other large French rivers (Seine and Loire rivers). In particulate phase, Ca, Sr, U, Pb, Bi, Cd, Sb and Zn displayed high enrichment factors over shale composition. Lead, Bi, Cd and Zn enrichment could be related to the anthropogenic inputs, while Ca, Sr and U enrichment was explained by lithological composition of the Rhône basin dominated by carbonate rocks. Distribution coefficients of elements (Kd) are relatively stable with however some variations with increasing SPM concentrations. These variations were attributed to local and diffuse inputs and to a higher contribution of carbonate bedrock in the Rhône basin during flood events. Dissolved and particulate major and trace elements, and suspended particulate matter (SPM) fluxes of the Rhône River to the Mediterranean Sea were estimated for the period 2001–2003. SPM and particulate element fluxes were highly dependent on flood events: 69 to 91% of the annual fluxes were exported in less than 12% of the time. Rhône River inputs were the principal source of particulate elements (except for Cd and Zn) in the north-western Mediterranean Sea, while the major part of dissolved elements were carried out by atmospheric inputs except dissolved As, for which Rhône River contributed to more than 50% of the input to the marine system.

Average composition of basic magmas and mantle sources of island arcs and active continental margins estimated from the data on melt inclusions and quenched glasses of rocks

Based on the generalization of data on melt inclusions and quenched glasses, the average compositions of subduction (island arc and active continental margin settings) basic magmas were estimated. The main geochemical features of the average composition of these magmas are significant depletion in Nb and Ta, less significant depletion in Ti, Zr, and Sm, and enrichment in Cl, H2O, F, and P in the primitive mantlenormalized patterns. The average normalized contents of moderately incompatible HREE in these magmas are close to those in the basic magmas of other geodynamic settings. Subduction basic magmas exhibit negative correlation of Li, Y, Dy, Er, Yb, Lu, and Ti contents with MgO content. Most of incompatible elements (Nb, Ta, U, Th, LREE) do not correlate with MgO, but correlate with each other and K2O. Variations in element contents are related to crystallization differentiation, magma mixing, and possibly, participation of several sources. The water content in the island arc basic magmas varies from almost zero value to more than 6 wt %. Most compositions are characterized by weak negative correlation between H2O and MgO contents, but some compositions define a negative correlation close to that in magmas of mid-ocean ridges (MOR). Considered magmas demonstrate distinct positive correlation between MgO content and homogenization temperature, practically coinciding with that of MOR magmas. Modeling of phase equilibria revealed widening of crystallization field of olivine in the magmas of subduction zones compared to MOR magmas. This can be related to the high water content in subduction magmas. Simultaneous liquidus crystallization of olivine and clinopyroxene in subduction magmas occurs at pressure approximately 5 kbar higher than that of MOR magmas. Based on the average ratios of trace element to K2O content, we determined the average compositions for subduction magma sources. Relative to depleted mantle, they are enriched in all incompatible elements, with positive anomalies of U, Rb, Ba, B, Pb, Cl, H2O, F, and S, and negative anomalies of Th, K, Be, Nb, Ta, Li, Nd, Pb, and Ti. A general elevated content of incompatible elements indicates a reworking of the rocks of mantle wedge by fluids and melts that were released from the upper layers of subducted plate.

Syngenetic phlogopite inclusions in kimberlite-hosted diamonds: implications for role of volatiles in diamond formation

We discuss the chemistry of exceptionally rare phlogopite inclusions coexisting with ultramafic (peridotitic) and eclogitic minerals in kimberlite-hosted diamonds of Yakutia, Arkhangelsk, and Venezuela provinces. Phlogopite inclusions in diamonds are octahedral negative crystals following the diamond faceting in all 34 samples (including polymineralic inclusions). On this basis phlogopite inclusions have been interpreted as syngenetic and in equilibrium with the associated minerals. In ultramafic diamonds phlogopites coexist with subcalcic high-Cr 2O 3 pyrope and/or chromite, olivine and enstatite (dunite/harzburgite (H) paragenesis) or with clinopyroxene, enstatite, and/or olivine and pyrope (lherzolite (L) paragenesis). Ultramafic phlogopites have high Mg# [100⋅Mg/(Mg+Fe)] from 92.4 to 95.2 and Cr 2O 3 higher than TiO 2 in H-phlogopites (1.5–2.5 wt.% versus 0.1–0.4 wt.%, respectively) but lower in L-phlogopites (0.15–0.5 wt.% versus 1.3–3.5 wt.%, respectively). Eclogitic (E) phlogopites show Mg# from 47.4 to 85.3 inclusive, and very broad ranges of TiO 2 up to 12 wt.%. The primary syngenetic origin of phlogopite is indicated, besides other factors, by its compositional consistency with the associated minerals. The analyzed phlogopites are depleted in BaO (0.10–0.79 wt.%), and their F and Cl contents are highly variable reaching 1.29 and 0.49 wt.%, respectively. The latter is in line with high Cl enrichment in some unaltered kimberlites and in nanometric fluid inclusions from diamonds. The presence of syngenetic phlogopite in kimberlite-hosted diamonds provides important evidence that volatiles participated in diamond formation and that at least a part of diamonds may have been related to early stages of kimberlites formation.

Groundwater geochemical evolution in the northern portion of the Guarani Aquifer System (Brazil) and its relationship to diagenetic features

The groundwater flow pattern in the northern portion of GAS (Guarani Aquifer System) is characterized by the existence of four regional recharge areas located in São Paulo, Mato Grosso do Sul and Goiás states. From these areas of recharge the regional flow is radial and directed toward the center of the Paraná Sedimentary Basin. Local discharge occurs in portions of outcrop regions. The groundwater has low mineralization and can be classified as Ca or Ca–Mg–HCO3 type, Na–HCO3 type and Na–HCO3/Cl/SO4 type, this sequence represents the hydrochemical evolution. The mechanisms responsible for this evolution are dissolution of feldspars and removal of the carbonate cement from the sandstone mineral framework, followed by ion exchange, responsible for the increase in the Na concentration and decrease of Ca, and, finally, enrichment in Cl and SO4 derived from underlying aquifer units. The hydrochemical evolution is consistent with diagenetic features that are observed in the sandstones, with the presence of siliceous cement in the outcrop areas, and carbonate cement toward the center of Paraná Basin.

Hydrogeological framework and occurrence of groundwater in the Ethiopian aquifers

Comprehensive hydrogeological investigations have been carried out in the Ethiopian volcanic terrain and associated quaternary sediments. The occurrence and distribution of groundwater are systematically analysed in relation to the geomorphological and geological setting within one of the world’s thickest volcanic provinces. The study starts from regional conceptualization to a more focussed analysis of four selected areas with distinct hydrogeological features. The chosen areas represent highland trap volcanic sequence characterized by multi-layer aquifers, intermountain sedimentary graben, fractured rift floor volcanics boarded by steep high-altitude plateau, and vast rift floor flood plain covered with alluvial sediment with adjoining gently-sloping pediments. The result revealed extreme variations in aquifer hydraulic characteristics and recharge rates. The flow and occurrence of groundwater is strongly controlled by the structure and geomorphological setup of the volcanic rocks and associated sediments. Groundwater flow in the rift and escarpment areas is largely controlled by faults. The recharge varies in a wide range between a few mm to 400 mm/yr. Despite the occurrence of permeable rocks and high recharge rates in some highlands adjacent to steep escarpments, the groundwater reserve is low due to the fast release of the recharged water to the rift plains through large open faults. Wide basic and acidic volcanics, alluvio-colluvial and lacustrine deposits form shallow unconfined aquifers, with transmissivity varying between 27 and 135 m 2/d. The thick trap series volcanics interbedded with river gravels and sands form deep confined and semi-confined aquifers locally with artesian conditions. Intermountain grabens and rift floor sediments associated with fractured volcanics form the largest aquifers under water table and semi-confined conditions. High well yields in deeper volcanic aquifers are often associated with regional fault lines and permeable sediments interbedded with the volcanics. Limited water quality analysis indicates that the groundwaters are Ca–MgHCO 3 type in the highlands, Na–HCO 3 type in the rift with local SO 4 and Cl enrichment. Hard waters are dominant in the basic volcanics. The highland waters have relatively lower ionic concentration (TDS ranging from 50 to 1200 mg/l). The rift waters have high salinity and fluoride, which is the major national water quality problem.

The role of mantle-derived volatiles in the petrogenesis of Palaeoproterozoic ferropicrites in the Pechenga Greenstone Belt, northwestern Russia: Insights from in-situ microbeam and nanobeam analysis of hydromagmatic amphibole

New in-situ trace element and hydrogen isotopic data of hydromagmatic amphiboles from ferropicritic gabbro–wehrlite intrusions and lava flows of the Palaeoproterozoic Pechenga Greenstone Belt (Russia) provide insights into the controversial source of volatiles that are implicated in Precambrian ultramafic magmatism. The intrusions mainly contain oikocrystic kaersutites and pargasites, whereas lava flows generally include idiomorphic Fe-kaersutites and Fe-pargasites. All orthomagmatic amphiboles display slightly LREE-enriched chondrite-normalised patterns. Primitive mantle-normalised patterns of amphiboles from the intrusions display positive Nb–Ta, moderate negative Th–U and distinctive negative Sr–Li anomalies. Conversely, Fe-kaersutites and Fe-pargasites from the lava flows display undepleted Th, U, Sr and Li signatures. Boron and Cl enrichment is primarily observed in secondary edenites, which locally rim orthomagmatic kaersutites. In-situ δD measurements of hydromagmatic amphiboles from the gabbro–wehrlite intrusions display values ranging between −70‰ and −170‰, and total water contents between 1 and 3 wt.%. Conversely, primary hydromagmatic amphiboles from the Pechenga flows display lighter δD compositions ranging between −100‰ and −270‰, and lower (<2 wt.%) total water contents.The Ti– and Nb–Ta-enriched nature of hydromagmatic amphiboles from the intrusions and lava flows indicates that the source of volatiles in the Pechenga ferropicrites could be either a metasomatised subcontinental mantle or a volatile-bearing plume. Positive Nb–Ta/La anomalies in amphiboles from the intrusions rule out crustal contamination with granitoid crust during petrogenesis and emplacement as the main source of the volatiles. Local B–Cl enrichment suggests that some samples may have interacted with hydrothermal fluids. The range of in-situ δD values in hydromagmatic amphiboles is consistent with the presence of magmatic water. The lighter hydrogen isotopic composition and lower water contents of the primary igneous amphiboles from the lava flows compared to amphiboles from the intrusions indicate that the lava flows degassed upon emplacement.Previous studies investigating the role of volatiles in Precambrian ultramafic magmatism preferentially collected data from thin lava flows, whereas thicker flows or intrusions have been generally neglected. We emphasise the necessity to re-evaluate the controversial role of volatiles in the petrogenesis of ultramafic magmas by investigating evidence from thicker flows or intrusions, which may have retained their full volatile budget.

Endogenous transformations of kotoite in calciphyres at magnesian-skarn deposits of boron

The succession of endogenic transformation of kotoite and accompanying minerals in marbles and calciphyres at hypabyssal magnesian-skarn deposits of boron is proved to be controlled by the anion composition of the hydrothermal solutions and the Mg mole fraction of the carbonate rocks. Early in the postmagmatic stage forming the B ore mineralization, the solutions contain Fe and F, as is reflected in the formation of kotoite and suanite in association with clinohumite, phlogopite, and Al-and Ti-bearing Mg-Fe borates, such as magnesiohulsite and magnesioludwigite. An increase in the F concentration of the hydrothermal solutions stimulates the formation of humites (from clinohumite to chondrodite and norbergite), which are replaced in the presence of kotoite by pertsevite (a hydroxofluorosilicateborate). In the calciphyres of Mount Brooks, Alaska, and at other deposits, the latter mineral is rock-forming in kotoite-clinohumite calciphyres, replaces this association, and is accompanied by fluoborite, nocerite, and fluorite. The further compositional transformations of the solutions with their enrichment in Cl result in the replacement of kotoite marbles and calciphyres and adjacent periclase marbles by sakhaite rocks with newly formed karlite. The neutralization of the hydrothermal solutions and their simultaneous cooling control the replacement of kotoite rocks by borcarite. The endogenic transformations of kotoite end with its szaibelyitization and/or brucitization and the simultaneous development of wightmanite in the marbles and the subsequent carbonatization of the borates. The research was carried out with the use of the author materials from boron deposits in Russia, Korea, Romania, England, France, and the United States.

RELATIVE TIMING OF ALBITIZATION AND CHLORINE ENRICHMENT IN BIOTITE IN PROTEROZOIC SCHISTS, SNAKE CREEK ANTICLINE, MOUNT ISA INLIER, NORTHEASTERN AUSTRALIA

In the Snake Creek area, near Cloncurry, Mount Isa Inlier, in northeastern Australia, multiple episodes of deformation, lowpressure metamorphism, intrusion of abundant mafic and granitic bodies, and extensive metasomatism occurred throughout the Mesoproterozoic Isan Orogeny. Albitites and associated metasomatic biotite-rich schists are abundant in the core of the Snake Creek Anticline, and are concentrated in five areas. Albitization peaked during D1 and was commonly localized along shear zones. Muscovite schists adjacent to albitites were altered to albite-bearing biotite-rich schists. Porphyroblast growth in metasomatic rocks commenced with cordierite and andalusite from late syn-D1, but episodic growth continued to post-D5, with the peak of metamorphism occurring late syn-D3 to early syn-D4. The timing of albitization was determined from the presence or absence of albite in various stages of andalusite growth, and similarly the Mg# [Mg/(Mg + Fe)] and Cl contents of biotite were examined over the span of porphyroblast-growth history. Differential mass-transport of Mg and Fe took place from the albitites to the adjacent schists predominantly during D1, and the Mg# for biotite in metasomatic rocks was largely fixed during D1. The Cl content of the matrix biotite varies considerably in the different areas of albitite development, from below detection to a maximum of 1.5 wt%. This could indicate that the Cl enrichment event was not related to albitization, but there is nevertheless an overall spatial relationship between them. In any particular sample, the Cl content in biotite is generally higher in the matrix than for inclusions in late andalusite, with inclusions in early andalusite being the poorest in Cl. Enrichment of Cl in biotite is a function of f(HCl)/f(H2O) rather than salinity, and so could be related to the replacement of muscovite by albite, as this involves release of H + . The ratio f(HCl)/f(H2O) would have been low during periods of high flux of fluid that produced the albitites, but increased during low flux, in the waning stages of albitization, resulting in maximum enrichment in Cl relatively late in the metasomatic history.

HALOGEN VARIATIONS IN THE PALEOPROTEROZOIC LAYERED MAFIC-ULTRAMAFIC INTRUSIONS OF EAST KIMBERLEY, WESTERN AUSTRALIA: IMPLICATIONS FOR PLATINUM GROUP ELEMENT MINERALIZATION

A number of Paleoproterozoic layered mafic-ultramafic intrusions in the central part of the Halls Creek orogen of East Kimberley, Western Australia, have been explored for platinum group elements, chromium, nickel, copper, cobalt, and gold. Here we report on the halogen geochemistry of apatite and biotite in a number of these intrusions. Interstitial apatite is ubiquitous in these intrusions and, in most samples, tends to be relatively enriched in F and OH end members and relatively poor in Cl (<20 mole%). Fluorapatite occurs in the more evolved igneous rocks and in samples from the margins of the intrusions that apparently have been contaminated by metamorphic country rock. Cl/F ratios generally increase with bulk rock molar Mg/(Mg + Fe) ratios, as observed in other intrusions. Only a few samples show Cl enrichment as high as that seen in the Stillwater and Bushveld complexes beneath the major stratabound platinum group element deposits. The most Cl-rich compositions observed occur in the upper part of the Springvale intrusion, where it is associated with troctolite, and in a single sample from the McIntosh intrusion. For the former intrusion, it is suggested that volatiles migrating out of the lower part of the mafic stratigraphy stabilized olivine at the expense of pyroxene. Associated biotite tends to contain little (no more than 10 mole %) Cl or F. It is concluded that the East Kimberley intrusions contained a low to moderate volatile component that, during the combined processes of crystallization, degassing, and fractionation of interstitial halogen-bearing minerals, produced a late, mobile, interstitial silicate liquid or volatile-rich fluid phase of variable Cl/F content that in turn caused most of the observed variations within any given intrusion. The exceptions include the margins of the intrusions that appear to have been affected by country rocks, either during emplacement (assimilation) or during later metamorphism. Apatite’s generally low Cl/F ratio, the lack of primary amphibole, and the high background sulfur concentrations of the East Kimberley intrusions suggest that these magmas were relatively volatile poor. The development of high-grade, platinum group element-enriched horizons by late-stage hydrothermal processes that could have mobilized significant amounts of the platinum group elements and sulfur is considered to be unlikely.

Serpentinite Subduction: Implications for Fluid Processes and Trace-Element Recycling

Serpentinites are important components of the oceanic lithosphere and are viewed as major water sources in subduction zones. Study of a set of ultramafic rocks equilibrated at increasing subduction depths (oceanic and high-pressure antigorite serpentinites, olivine-orthopyroxene rocks), shows that these rocks can act as carriers of Cl, B, Sr, Rb, Cs, and alkalis. Serpentinization of the oceanic mantle produces enrichment in Sr, Cl, B, and alkalis. The subduction path within the stability field of antigorite serpentine is accompanied recycling of oceanic Cl, B, Sr, and alkalis into variably saline fluids (4-8 wt% NaClequiv based on mass balance calculations; 10 to 50 wt% NaClequiv based on fluid inclusion analysis). Fluids are produced during a first (olivine-in) dehydration reaction releasing a maximum amount of 2 wt% H2O. The oxygen isotope compositions of the high-pressure antigorite serpentinites largely mirror those of the pre-subduction protoliths. This is interpreted as a lack of re-equilibration due to limited fluid production and mobility during high-pressure metamorphism Breakdown of the antigorite serpentinites to olivine-orthopyroxene rocks releases 6.5 wt% H2O with formation of a low salinity fluid (0.4-2 wt% NaClequiv based on mass balance calculations). The salt contents of subduction fluids appear to decrease with increasing depth: a "differentiation" in the Cl content of fluids can thus be expected, with shallower saline fluids being followed by deeper, less saline, solutions. Primary fluid inclusions in olivine-orthopyroxene rocks represent remnants of the antigorite-breakdown fluid. Their trace-element compositions are enriched in several LILE (Rb, Sr, Cs, Pb), Li, B, and alkalis and are depleted in HFSE; their trace-element patterns are similar to those of many present-day arc lavas. Oxygen isotope compositions of olivine-orthopyroxene rocks are rather homogeneous, and are suggestive of larger fluid mobility during dehydration. The antigorite breakdown reaction appears to produce a mobile fluid that can play a role in the metasomatism of sub-arc mantle. Serpentinized oceanic mantle thus represents a valuable candidate reservoir for fluids and incompatible elements: consequently, its role in the overall element cycle in subduction settings should be re-evaluated.

Occurrence of Halogen‐rich Phlogopite in Late Cenozoic Volcanic Rocks in the Japanese Arcs

Abstract. Halogen‐rich phlogopite occurs in the groundmass of andesite and dacite lavas from Late Tertiary to Quaternary volcanoes associated with native sulfur and limonite deposits (Shiretoko‐Iwozan, Hachimantai, Adatara, Omeshidake, Masaki) and hydrothermal ore deposits (Harukayama, Muineyama, Hishikari) in Japan. The F contents of the halogen‐rich phlogopite range from 3.6 to 5.7 wt%, corresponding to atomic F/(F+C1+OH) ratios ranging from 0.45 to 0.69. On the other hand, the Cl contents of the halogen‐rich phlogopite are around 0.2 wt%. The atomic Mg/(Mg+Fe) ratios range from 0.69 to 0.83.The fluorine intercept value [IV(F)] defined by Munoz (1984) of the phlogopites ranges from 0.79 to 3.17, and the chlorine intercept value [IV(Cl)] ranges from ‐7.11 to ‐7.77. The observed IV(F) of the phlogopites broadly overlap the range of the IV(F) for biotites from porphyry copper deposits. On the other hand, the observed IV(Cl) are significantly lower than the IV(Cl) for biotites from porphyry copper deposits. Whereas the F contents of the phlogopite appear more prominent compared to the Cl contents, the calculation of halogen intercept values revealed that the phlogopites are enriched in Cl with respect to the element distribution effect of Mg‐Fe substitution. Since the degree of Cl enrichment of the phlogopite is more significant compared to that of biotite in porphyry copper deposits, the phlogopites are considered to have formed under the condition of significantly high activity of halogens. Hydrothermal ore deposits may be formed in magmatic hydrothermal system associated with volcanoes where halogen‐rich phlogopite is formed by hypersaline fluid.

Ultra-high chlorine in submarine Kı̄lauea glasses: evidence for direct assimilation of brine by magma

Basaltic glass grains from the submarine south flank of Kı̄lauea, Hawai′i, have Cl concentrations of 0.01–1.68 wt%, the latter being the highest Cl content yet recorded for a Hawaiian glass. The high-Cl glass grains are products of brine assimilation by tholeiite magma. The glasses are grains in a sandstone clast from bedded breccias draping the southwestern margin of Kı̄lauea’s submarine midslope bench. The clast contains two distinct suites of glass grains: abundant degassed tholeiites, perhaps derived from subaerial lavas of Mauna Loa that shattered upon ocean entry, and a smaller population of Kea-type tholeiite (n=17 analyzed) that erupted subaqueously, based on elevated S (780–1050 ppm), H2O (0.42–1.27 wt%), and CO2 (<30–120 ppm), probably early in Kı̄lauea’s shield-building stage. Ten grains in this group have Cl>1000 ppm, six >5000 ppm, and two grains have >10 000 ppm dissolved Cl. Abundances of H2O, Na2O, K2O, and several trace elements increase regularly with Cl concentration, and we estimate that Cl enrichment was due to up to 13 wt% addition of a brine consisting of 78% H2O (wt), 13% Cl, 4.4% Na, 2.6% K, 2.6% Ca, 620 ppm Ba, 360 ppm Sr, 65 ppm Rb, and 7 ppm Pb. The large amounts of brine addition argue against bulk assimilation of low-porosity brine-bearing rock. The brine’s composition is appropriate for a seawater-derived hydrothermal fluid that reacted with basaltic wall rocks at T>100°C, losing Mg and S and gaining K, Ca, Rb, Ba, Sr, and Pb, followed by phase separation near 500°C and ∼50 MPa (5 km below sea level at hydrostatic pressure). Brine was assimilated at or near the depth it formed, as estimated on petrologic grounds, but under lithostatic conditions. The highest extents of assimilation either forced volatile saturation of the magma or enriched already coexisting magmatic vapor in H2O. Possible mechanisms for assimilation are: (1) forcible injection of brine into magma during bursting of overpressured pockets heated by new dikes, or (2) intrusion of magma into lenses or sills occupied by trapped brine.

Regional variation of formation water chemistry and diagenesis reaction in underpressured system: example from Shiwu depression of Songliao basin, NE China

Geochemistry of formation waters in the Shiwu depression of the Songliao basin, northeast China, shows a distinct variation in different pressured systems. The study area is composed of terrigeneous clastics in fluvial-lacustrine environments, which contain formation water with salinity ranging from less than 1000 to 12,000 mg/l. Water composition varies with depth and hydrochemical regions. In the underpressured strata deposited during the rifting period, formation water is characterized by water type of CaCl 2 with higher salinity. NaHCO 3-dominanted water with lower salinity occurs in the normally pressured strata deposited during the post-rifting period. In the transition area between the normally pressured and underpressured zones, total dissolved solid (TDS) content ranges from 1000 to 7600 mg/1 and increases with depth. In this halite-free basin, brackish water may be attributed to the evaporation of formation water and water-rock interaction. In the deep buried underpressured water, a predominated diagenesis reaction resulting in Ca and Cl enrichment and reduction of Na may be related to albitization of plagioclase following the basinal fluid line (BFL). The results of this study indicate that salinity variation of formation water and diagenesis reaction is closely related to hydrochemical environments within different pressured systems.