Mass Change Calculations Research Articles

Erratum to: Mobilization and redistribution of major and trace elements in a lateritic profile: the Sheikh-Marut deposit, NW Iran

The Sheikh-Marut deposit is one of typical REE-rich lateritic deposits of Permian age in northwest of Mahabad, NW Iran. In this study, using geochemical techniques for calculation of mass changes and correlation coefficients, the effective factors in mobilization and redistribution of major and trace elements during lateritization processes across a selected profile were considered. Based upon TOC (total organic carbon) values, the ores across the profile were divided into two parts: (1) TOC-rich in the upper part and (2) TOC-poor in the lower part of the profile. Mass change calculations illustrated that elements such as Al, Fe, Ti, Th, V, Ni, Co, Cr, Be, Nb, Zr, Hf, Ta, and Sn were leached out from the TOC-rich part and were added to the TOC-poor section during lateritization processes. In addition, elements like Ca, K, Mg, Na, P, Pb, Cu, Zn, Cs, Y, Rb, Sr, Ba, and U were leached out from both the TOC-rich and the TOC-poor sections of the profile, and elements such as Mn, As, Cd, Tl, and Ga were enriched during lateritization. Incorporation of the results obtained from mass change calculations and correlation coefficients among elements demonstrated that factors such as presence or absence of organic ligands, physico-chemical conditions (Eh and pH) of depositional environment, and mineral control are three principal factors dominating leaching and redistribution of major and trace elements in the studied lateritic profile. The obtained results also revealed that scavenging by metallic oxides was rather more effective than adsorption mechanism in concentration of most trace elements in the studied ores.

Mineralogical and geochemical evolution of the Fusui bauxite deposit in Guangxi, South China: From the original Permian orebody to a Quarternary Salento-type deposit

Two types of bauxite deposits have been discovered in the Fusui area, Guangxi Province, South China. The original Permian bauxite occurs on the unconformity between the Middle Permian Maokou Formation and the Upper Permian Heshan Formation. The Salento-type (or karstic accumulational) bauxite is composed of the Quaternary incompact sediments that transformed from the original Permian bauxite. Samples were collected from two drilling cores and two profiles in study area, and field observations and mineralogical and geochemical analyses are integrated to reconstruct the metallogenic process from the original Permian bauxite to the Quaternary Salento-type bauxite. In the Permian lateritization and bauxitization, alkali metals and alkali earth metals are preferentially dissolved and removed from the parent rocks due to the intense chemical weathering; other major elements from the original profile are also depleted, as shown by the mass-change calculation result. Elements with a low mobility (e.g., Ti, Zr, Cr, Nb and V) are positively correlated with Al. When the bauxite deposit is affected by the modern groundwater system in the near-surface environment, the elements in the deposit display varied mobility due to the leaching intensity and the drainage conditions. After the bauxite ore horizons are exposed in the surface environment, impurities (primarily Fe and Si) are removed from the profiles, and Al is enriched; the clay minerals (kaolinite and chlorite) in the ores convert into aluminum minerals (boehmite and diaspore). When the exposed original bauxite orebodies break down and accumulate as bauxite gravel in the modern karstic depressions, the Salento-type bauxite deposits appear, and the ore quality is further improved. The intensity of the leaching process and the drainage conditions are the most important factors that control the ore quality during the ore-forming process that converts the original bauxite into the Salento-type bauxite.

Sensitivity of Goce Gradients on Greenland Mass Variation And Changes in Ice Topography

Abstract The Gravity field and steady state Ocean Circulation Explorer (GOCE) maps variations in the gravity field by observing second order derivatives (gradients) of the Earth gravitational potential. Flying in the low altitude of 255 km and having a spatially dense data distribution of short wavelengths of the gravity field, GOCE may be used to enhance the time varying gravity signal coming fromthe GRACE satellites. The GOCE gradients may potentially be used for the determination of residual masses in local regions. This can be done using Least-Squares Collocation (LSC) or the Reduced Point Mass (RPM) method. In this study, different gravity field solutions are calculated by the use of RPM, LSC and GOCE gradients, respectively. Gravity field time series are created and presented for the six consecutive months of GOCE gradient observations, data being acquired between November 2009 and June 2010. Corresponding gravity anomaly results are used for the calculation of ice mass changes by the use of theRPMmethod. The results are then compared with the computed topographic effect of the ice by the use of a modified topographic correction and the Gravsoft TC program. The maximal gravity changes at the ground predicted from GOCE gradients are between 2 and 4 mGal for the period considered. The gravity anomaly estimation error arising from the GOCE gradient data using only Tzz with an associated error of 20 mE is 11 mGal. This analysis shows the potential of using GOCE data for observations of ice mass changes although the GOCE dataset is limited to only six months. We expect four years of GOCE gradient observations to be available by mid-2014. This will increase the accuracy and spatial resolution of the GOCE measurements, which may lead to an accuracy necessary for observing ice mass changes.

Mass Change Calculation of the Bauxite in the WZD Area, Northern Guizhou, China

Through mass change calculation of the bauxite in the Wuchuan-Zheng, an-Daozhen (WZD) area to reveal the migration regular of elements in the ore-forming process: major elements all have loss except aluminum element which keep steady in the ore-forming process of the WZD bauxite deposit; Major elements in the upper and middle part of the profile have a large scale of runoff, in the lower part of the profile just have a small scale of runoff, and some elements concentrated in the lower part of the profile, above all of these shows that major elements have a downward moving trend. Alkaline metal have the largest scale of runoff demonstrated that the ore-forming environment is acidic.

The lateritic profile of Balkouin, Burkina Faso: Geochemistry, mineralogy and genesis

This study reports on the geochemical and mineralogical characterization of a lateritic profile cropping out in the Balkouin area, Central Burkina Faso, aimed at obtaining a better understanding of the processes responsible for the formation of the laterite itself and the constraints to its development. The lateritic profile rests on a Paleoproterozoic basement mostly composed of granodioritic rocks related to the Eburnean magmatic cycle passing upwards to saprolite and consists of four main composite horizons (bottom to top): kaolinite and clay-rich horizons, mottled laterite and iron-rich duricrust. In order to achieve such a goal, a multi-disciplinary analytical approach was adopted, which includes inductively coupled plasma (ICP) atomic emission and mass spectrometries (ICP-AES and ICP-MS respectively), X-ray powder diffraction (XRPD), scanning electron microscopy with energy dispersive spectrometry (SEM-EDS) and micro-Raman spectroscopy.The geochemical data, and particularly the immobile elements distribution and REE patterns, show that the Balkouin laterite is the product of an in situ lateritization process that involved a strong depletion of the more soluble elements (K, Mg, Ca, Na, Rb, Sr and Ba) and an enrichment in Fe; Si was also removed, particularly in the uppermost horizons. All along the profile the change in composition is coupled with important changes in mineralogy. In particular, the saprolite is characterized by occurrence of abundant albitic plagioclase, quartz and nontronite; kaolinite is apparently absent. The transition to the overlying lateritic profile marks the breakdown of plagioclase and nontronite, thus allowing kaolinite to become one of the major components upwards, together with goethite and quartz. The upper part of the profile is strongly enriched in hematite (+kaolinite). Ti oxides (at least in part as anatase) and apatite are typical accessory phases, while free aluminium hydroxides are notably absent. Mass change calculations emphasize the extent of the mass loss, which exceeds 50wt% (and often 70wt%) for almost all horizons; only Fe was significantly concentrated in the residual system.The geochemical and mineralogical features suggest that the lateritic profile is the product of a continuous process that gradually developed from the bedrock upwards, in agreement with the Schellmann classic genetic model. The laterite formation must have occurred at low pH (⩽4.5) and high Eh (⩾0.4) values, i.e., under acidic and oxidizing environments, which allowed strongly selective leaching conditions. The lack of gibbsite and bohemite is in agreement with the compositional data: the occurrence of quartz (±amorphous silica) all along the profile was an inhibiting factor for the formation of free aluminium hydroxides.

Geochemical characteristics of Kanigorgeh ferruginous bauxite horizon, West-Azarbaidjan province, NW Iran

Ferruginous bauxite horizon of Kanigorgeh is located ~ 20 km northeast of Bukan, West- Azarbaidjan province, northwest Iran. The horizon is a part of the Irano-Himalayan karst bauxite belt that was developed in a form of 8 discontinuous stratified layers and lenses varying in thicknesses (5-17 m) with extending over 3.2 km along the contact of Permian carbonates, Triassic dolomites. In this study, parental affinity and controlling factors of elements distribution in the bauxite ores are surveyed by applying analytical mineralogy, mass and volume changes calculations (method of isocon), elemental ratios, and correlation coefficients. Mineralogical analyses reveal that diaspore, hematite, and kaolinite are the major minerals in the ores with lesser and variable amounts of boehmite, goethite, muscovite-illite, rutile, and montmorillonite. In contrast to the presence of diasporic-boehmitic mineralogical composition in ores, the geochemical data (i.e., ratios of Pb/Y, Ga/Pb, Zr/Pb, and Cr/Ni), testify to gibbsitic composition for the original aluminum hydroxides. Microscopic studies and geochemical characteristics of major and trace elements indicate that the ores were formed authigenically by the alteration and weathering of basaltic parent rocks. Mass change calculations suggests that enrichment of many elements in the ores resulted by losing Si, Ca, K, Na, Mg, and P during weathering of plagioclase, K-feldspar, ferromagnesians, and apatite. In addition, variable amounts of Co, Sr, and Ba were lost during bauxitization. Geochemical considerations prove that distribution of major, minor, trace, and rare earth elements in the studied ores were principally controlled by factors such as cation exchanges, adsorption, increasing of pH in weathering solutions due to buffering by carbonate bedrocks, scavenging by Fe-oxides and hydroxides, isomorphic substitutions, co-precipitation, and differences in stability of primary minerals.

Geological and geochemical evolution of the Bolkardaği bauxite deposits, Karaman, Turkey: Transformation from shale to bauxite

The Bolkardağı bauxite province is located in the Tauride Belt of southern Turkey. The region hosts many lateritic- and karstic-type bauxite deposits within the Bolkardağı Unit (BU), the Namrun Tectonic Unit (NTU) and the Aladağ Unit (AU). The lateritic-type deposits occur on the Upper Triassic sericite-chlorite schist of the BU, on the Lower Triassic slates, and on the Upper Triassic phyllites of the NTU. The gradual transition from the protolith to saprolite and, eventually, to bauxite is observed in the lateritic-type deposits in the field. The karstic-type deposits occur in the carbonates of the BU, the NTU and the AU and were accumulated by clastic transportation from the lateritic material. The deposits within the BU and the NTU are metamorphosed and consist mainly of diasporite, haematite, pyrophyllite, chlorite, chamosite, and anatase; the deposits within the AU are not metamorphosed and consist mainly of boehmite and kaolinite, haematite, goethite, chlorite and anatase.The mean compositions of the deposits are 53% Al2O3, 19% Fe2O3, 12% SiO2, and 3% TiO2. The lateritic-type deposits have higher silica content (e.g., Camızalanı Bauxite Zone; mean 21% SiO2) than the karstic-type, indicating higher mobilisation of silica in the karstic-type deposits because of alkaline pH conditions. The ΣREE content varies between 273ppm and 1693ppm, and the ΣREE content increases with an increase in the content of La, Ce and Nd. The mass change calculations according to the Ti index element show that Rb, K, Ba, Ce, Si, Y, Sr, P, Ca, Mg and U were mobile during the bauxitisation processes. The Zr, Ta, Nb and Hf elements are relatively immobile in the first stage of bauxitisation in the saprolite zone but were slightly mobile at a later stage of bauxitisation. Fe, V, Pb, Ni, and Cr are the elements that were gained in the bauxite zone.From field evidence and geochemical data, it is concluded that the first stages of bauxitisation in the Bolkardağı Bauxite Province started during the post-Upper Triassic by the formation of a kaolinite-rich bauxitic soil via chemical weathering of the Lower Triassic pelitic rocks and Upper Triassic shales under acidic conditions. The kaolinite-rich bauxitic soil was transformed to boehmite during low water activity in hot and humid climatic conditions. The Aalenian–Bajocian transgression submerged the bauxite, causing burial diagenesis. At the time of the closure of the Tethyan Ocean during the Upper Cretaceous, ophiolite obductions over the continent gave rise to imbrication and further burial of the bauxite-bearing units. During this time, the bauxite deposits and their host units underwent a very low grade metamorphism in relation to their burial depths and thrusting. Thus, kaolinite was transformed to dickite, nacrite and pyrophyllite at 240–260°C in the saprolite zone, and boehmitic bauxite was transformed to diasporite in the deeply buried BU and the NTU. The boehmite was preserved as a primary bauxite mineral in the deposit which avoided burial metamorphism in the uppermost tectonic unit, the AU.

Rare Earth Elements Geochemistry of Sheikh‐Marut Laterite Deposit, NW Mahabad, West‐Azarbaidjan Province, Iran

AbstractLaterite deposit at Sheikh‐Marut (NW Mahabad, West‐Azarbaidjan province, Iran) occurred within middle–upper Permian carbonate rocks. It consists of seven stratiform and/or discontinuous lenticular layers extending over 4.2 km in length and having thicknesses ranging from 3 to 14 m. Mineralogical data show that the ores contain kaolinite and hematite as major and boehmite, diaspore, halloysite, amesite, anatase, and muscovite‐illite as minor mineral phases. The computed Ce anomaly values in the ores range from 0.05 to 20.84. Conservative index (e.g., Eu/Eu*) suggests that this deposit is a product of alteration and weathering of basaltic rocks. Rhythmic increment of ΣREE values of the ores with approaching to the carbonate bedrocks shows an in‐situ occurrence of lateritization processes. Mass change calculations of elements indicate that two competing processes namely leaching and fixation were the major regulating factors in concentration variation of REEs (La–Lu) in this deposit The obtained results show that pH increase of weathering solutions by carbonate bedrocks, existence of organic matters, and the degree of comlexation with organic ligands played remarkable role in distribution of REEs during lateritization. Further geochemical considerations revealed that secondary phosphates, Mn‐oxides and ‐hydroxides, diaspore, and anatase were the potential hosts for REEs in this deposit.

Uncertainty assessment of multi-temporal airborne laser scanning data: A case study on an Alpine glacier

In glaciology, volumetric changes from multi-temporal digital elevation models (DEMs) serve to validate and calibrate glacier mass balances from traditional in situ measurements. In this study, we provide a thorough uncertainty assessment of multi-temporal airborne laser scanning DEMs based on: (a) applying a statistical error model, (b) comparing laser echoes to reference points and surfaces, and (c) developing a physical error propagation model. The latter model takes into account the measurement platform characteristics, components of the measurement process, and the surface properties. Such a model allows the estimation of systematic and stochastic uncertainties for single laser echoes, as well as for distributed surfaces in every part of the study site, independent of the reference surfaces. The full error propagation framework is applied to multi-temporal DEMs covering the highly undulating terrain in the Findelengletscher catchment in Canton Valais, Switzerland. This physical error propagation model is able to reproduce stochastic uncertainties in accordance with measurements from reference surfaces. The high laser point density in the study site reduces the stochastic uncertainties over the whole glacier area to negligibly small values. However, systematic uncertainties greatly influence the calculation of mass changes and lead to corrections of the thickness change of up to 35%.

Geological, geochemical, and mineralogical characteristics of the Mandan and Deh-now bauxite deposits, Zagros Fold Belt, Iran

The Mandan and Deh-now bauxite deposits are located 40km northeast of the Dehdasht city in the Zagros simply fold belt. These deposits occur in eroded major NW–SE trending anticlines and occupy karst cavities near or at the boundary between the Sarvak and Ilam Formations. Local uplifts at the end of the Cenomanian and the mid-Turonian caused erosion and karstification of the Sarvak Formation. These unconformities in the Upper Cretaceous favoured the formation and enrichment of bauxite deposits in the Zagros fold belt. The bauxite sequence in the Mandan deposit consists of white, gray, black, pisolitic, red, and yellow bauxites. This sequence was repeated in the Deh-Now area, but without gray and black bauxites. The present mineralogical studies of the Sarvak Formation and the Mandan and Deh-now bauxite deposits indicate oxidizing to reducing conditions during the Upper Cretaceous in the Zagros fold belt, which had a significant effect on the compositions of the bauxites. At least two phases of bauxitization can be distinguished in the study area: (i) an oxidizing phase represented by boehmite, diaspore, hematite and kaolinite; and (ii) a reducing phase represented by pyrite and chlorite. Geochemical data show that trace elements, like Zr, Hf, Nb, Ta, Th, and U, were enriched during bauxitization. The bauxite deposits and carbonate rocks show similar REE patterns, namely they are enriched in REEs although the LREEs are more enriched than the HREEs. Mass change calculations demonstrate that Mg, Mn, Ca, K, and P2O5 were leached out of the weathered system whereas Al, Fe, and Si become concentrated in the residual system. This study indicates that the Mandan and Deh-now deposits are karst-type bauxites formed by karstification and weathering of the Sarvak Formation.

Geology and Geochemistry of Highly Metamorphosed Footwall Alteration Zones in the Hongtoushan Volcanogenic Massive Sulfide Deposit, Liaoning Province, China

AbstractThe Hongtoushan Archean Cu–Zn volcanogenic massive sulfide (VMS) deposit, which was metamorphosed (3.0–2.8 Ga) to upper amphibolite facies at temperatures between 600 and 650°C, occurs in the Hunbei granite–greenstone terrane, Liaoning Province of NE China. Stratiform cordierite–anthophyllite gneiss (CAG) that occurs hundreds of meters below the ore horizon in the Hongtoushan district corresponds to the metamorphosed semi‐conformable alteration zone of the VMS hydrothermal system, whereas the CAG that contains abundant deformed sulfide‐bearing quartz veins immediately below the main ore layer represents the metamorphosed discordant alteration zone. Whole‐rock geochemistry indicates that stratiform CAG was derived ultimately from five lithologies (basalt, basaltic andesite, andesite, dacite, and rhyolite), while discordant CAG derived from a single lithology (rhyolite). Amphibolite and biotite‐rich gneiss are identified as a metamorphosed least‐altered precursor for these CAGs. Mass change calculation indicates that, compared to the least‐altered rocks, stratiform CAG is enriched in Fe and Mg, and depleted in Na, K, Ca, Cu, Pb and Zn, while discordant CAG is enriched in Fe, Mg, Si, Na, Pb, Cu and Zn, and depleted in K. HREE and HFSE (Zr, Ti, Nb and Ta) behaved inertly during submarine alteration, whereas Rb, Sr, Ba and LREE (especially Eu) were leached off.Both stratiform and discordant CAGs are depleted in 18O, with values up to 7‰ lower than their corresponding least‐altered precursors. Addition of Fe, Mg, and depletion of Ca, K, Sr, and 18O, indicate that hydrothermal alteration for both types of CAGs was characterized by chloritization prior to metamorphism. Stratiform CAG could be used to evaluate the mineralization potential of VMS in metamorphic terranes, while discordant CAG containing sulfide‐bearing quartz veins could be a good indication for overlying stratiform massive sulfide ores as well as an exploration target itself.

Geochemistry of Major, Trace, and Rare Earth Elements in Biglar Permo-Triassic Bauxite Deposit, Northwest of Abgarm, Ghazvin Province, Iran

Biglar Permo-Triassic bauxite deposit is located in ~15 km northwest of Abgarm, southwest of Ghazvin province, west of central Iran. It consists of 8 stratiform and discontinuous bauxite lenses lying along the contact of Ruteh (Permian) and Elika (Triassic) carbonate formations. Petrographically, the bauxite ores exhibit collomorphic-fluidal, pseudo-breccia, pseudo-porphyritic, panidiomorphic-granular, nodular, and skeletal textures indicative of authigenic origin. Weathering of andesitic parent rocks led to the formation of Ferruginous laterite, bauxitic clay, and siliceous bauxite. Mass change calculations of elements indicate that Si, and Ba were depleted during bauxitization and Al, Ti, Zr, Nb, Hf, Ga, U, Th, V, and Cr were enriched. However, Fe, Y, Rb, Sr, Co, Ni, LREEs, and HREEs experienced leaching-fixation mechanism during the development of the residual system. Based upon obtained data, the available organic matters, pH variations in weathering solutions, adsorption process, functioning of carbonate bedrock as a geochemical barrier, existing in resistant minerals, and fixation in the neomorphic phases have been shown to play significant role in distribution of trace and rare earth elements. Further geochemical considerations indicate that minerals such as monazite, rhabdophane, belovite, churchite, and xenotime are the potential hosts for rare earth elements in Biglar bauxite deposit.

Immobile elements and mass changes geochemistry at Sar-Faryab bauxite deposit, Zagros Mountains, Iran

The Sar-Faryab bauxite deposit is located in 250 km east of Ahvaz city in southwestern Iran. Structurally the deposit located in the Zagros Simply Folded Mountain Belt. Outcrops of the bauxite horizons in the area are distributed irregularly over an area of about 20 km 2 but have fairly uniform thickness averaging 1 to 1.5 m. The Sar-Faryab bauxite is situated in NW–SE trending Mandan anticline and occurs in karst horizons near or at the boundary between the Sarvak and Ilam Formations. Based on field observation, mineralogy and stratigraphy an unconformity during Cenomanian–Turonian times has exposed the Sarvak Limestone to karst weathering and the layers of Marly Limestone, Argillite, Oolitic–Pisolitic, Yellow, Red and White Bauxite were formed and accumulated in the karstic areas. This study uses the geochemistry of immobile elements to trace the precursor rock of the bauxite deposit and to calculate the mass changes that took place during weathering and bauxitization. In this way fifteen samples were collected from seven layers of the deposit for geochemical studies using XRF. Geochemical data show that Al and Ti were immobile during the bauxitization process and were used for mass change calculations. Mass changes were calculated from the concentration ratio of immobile elements for the different bauxite rocks and the Sarvak Limestone. As only one linear trend is evident in the Al–Ti binary diagram and the Sarvak Limestone coincides with this trend, we concluded that the source of the Sar-Faryab bauxite was the underlying Marly limestone (Sarvak Formation). The karst bauxite deposits are probably of authigenic origin, as evidenced by their geochemical characteristics, lithologic associations, textural and mineralogy.

Mass Change Calculations During Hydrothermal Alteration/Mineralization in the Porphyry Copper Deposit of Darrehzar, Iran

Mass Change Calculations During Hydrothermal Alteration/Mineralization in the Porphyry Copper Deposit of Darrehzar, Iran

Alteration Mineralogy and Geochemistry of the Hydrothermally Altered Rocks of the Kutlular (Sürmene) Massive Sulfide Deposit, NE Turkey

Volcanogenic massive sulfide deposits accompanying the Upper Cretaceous felsic rocks in the intra-arc rift zone of the Pontide palaeo-arc are common in the NE Turkey. One of them, the Kutlular (Sürmene, Trabzon) deposit, is an abandoned mine within the Upper Cretaceous mafic, felsic volcanics and subvolcanic rocks. Detailed mineralogical and geochemical studies indicate the presence of hydrothermal alteration zones around the Kutlular deposit; these alteration zones are represented by silicification-pyrite-illite zone, illite-silicification zone, illite/smectite-silicification zone, smectite zone accompanying kaolinite and halloysite in the dacitic pyroclastics, and additionally chlorite zone in the mafic volcanics. Lithogeochemical data indicate that the footwall dacitic rocks (Zr/Y= 1.39-16.39, La/Yb= 0.14-9.57) and hanging-wall basalts-basaltic andesites (Zr/Y= 2.13-5.65, La/Yb= 1.16-5.00) are transitional between tholeiitic and calc-alkaline in character. The trace element patterns of the rocks show considerable LILE enrichment (K, Rb and Ba) and depletion in Sr and Ti relative to N-type MORB. Chondrite-normalized REE patterns of the footwall show pronounced HREE enrichment. The Kutlular footwall and hanging wall alteration zones have several geochemical characteristics that show systematic changes with increasing proximity to ore body such as Na depletion as well as elevated alteration index (AI) and chlorite-carbonate-pyrite index (CCPI). Generally, hanging-wall mafic volcanics and footwall rocks have high CCPI (chlorite-carbonate-pyrite index) values, indicating the importance of chlorite and pyrite formation in these rocks. Calculated mass changes in the footwall dacites commonly are large, and result from major silica mass transfer (-9.11 to 99.68 g/100 g rock). Mass-change calculations indicate that CaO + Na_2O + MgO were leached from the rocks by hydrothermal solutions, whereas large amounts of hydrothermal iron were added. Hanging wall basalt and basaltic andesite shows mass changes that are generally much smaller than in the footwall.

Geochemistry and Stable Isotope Composition of Altered Rocks at the Golden Cross Epithermal Au-Ag Deposit, New Zealand

Golden Cross is a late Miocene volcanic-hosted epithermal Au-Ag deposit associated with quartz ± calcite ± adularia ± illite assemblages located in the Coromandel peninsula, New Zealand. Gold- and Ag-bearing quartz veins occur in intensely altered flows and lesser pyroclastic volcanic rocks of andesitic and dacitic composition. The primary control of whole-rock geochemistry at Golden Cross, as at other volcanic-hosted epithermal deposits associated with quartz ± calcite ± adularia ± illite assemblages, is the destruction of igneous plagioclase by hydrothermal alteration and K metasomatism from hydrothermal fluids. Quantitative mass change calculations indicate that, irrespective of the rock type (andesite versus dacite), hydrothermally altered rocks are enriched in K, Rb, As, and Sb around the Empire vein system and stockwork. In contrast, Na and Sr are strongly depleted around the veins, with Fe locally depleted. Silicon, Ca, Mg, and Ba are variably enriched and depleted, with Si enriched immediately adjacent to the veins and Ca only locally enriched. The enrichment and depletion trends for these elements are directly related to the degree of alteration and the alteration mineralogy. Intensely altered rocks show addition of K and Rb, coupled with loss of Na and Sr, which reflect the replacement of plagioclase by adularia and/or illite. Calcium depletion also reflects the destruction of plagioclase, although Ca loss is locally offset by the formation of hydrothermal calcite. Progressively higher Na and Sr away from the veins reflect greater preservation of plagioclase and the transition into less altered rocks on the margins. Potassium, Rb, Na, and Sr all define anomalies that extend 200 to >350 m east of the veins and are more widespread than As and Sb, which are anomalous within 150 to 200 m of the veins. The geochemical zonation patterns identified at Golden Cross are very similar to those at other epithermal deposits associated with quartz ± calcite ± adularia ± illite assemblages. Potassium, Na, Rb, Sr, and Ca enrichment and depletion patterns provide insight into the intensity and type of alteration, thereby complementing traditional analyses of Au, Ag, and other pathfinder elements, such as As and Sb, that are used to explore for epithermal Au-Ag deposits. Potassium, Na, Rb, Sr, and Ca enrichment and depletion patterns at Golden Cross are larger than halos defined by precious metals and other trace element pathfinders, thereby providing a larger target area for exploration. Potassium metasomatism is particularly important because the Empire vein system occurs in altered rocks that are significantly enriched in K. Potassium metasomatism can be evaluated by raw K 2 O data or, more effectively, by K mass changes, molar element ratios of (2Ca + Na + K)/Al versus K/Al (wt % K 2 O * 100)/ppm Sr, Rb/Sr ratios, and K numbers [K/(2Ca + K + Na) molar]. Whole-rock oxygen isotope patterns at Golden Cross are similar to those described at other epithermal deposits associated with quartz ± calcite ± adularia ± illite assemblages. However, the area defined by low δ 18 O values is smaller than the area that can be defined by field mapping of alteration minerals or whole-rock major and trace element geochemistry.

Mass Change Calculations as Applied to the Search for Volcanogenic Massive Sulfide Deposits: An Example from Malusok, Siocon, Zamboanga del Norte, Mindanao, Philippines

Abstract. The Malusok volcanogenic massive sulfide (VMS) deposits comprise two adjacent ore bodies, the Main Malusok and the Malusok Southeast ore bodies, hosted within Cretaceous metamorphic rocks. Owing to the structural and metamor-phic overprinting combined with intense hydrothermal alteration, primary textures of the Malusok volcanic rocks have been obliterated. The stratigraphic correlation of the Main Malusok and the Malusok Southeast ore bodies show that both deposits are essentially confined within a single stratigraphic interval. The lithogeochemical analysis of the Malusok samples shows that constituent lithologies have precursor compositions ranging from sub-alkaline basalts to rhyodacites. Field and mass flux data suggest that the Main Malusok VMS deposits were derived as a consequence of axial hydrothermal activity. The Malusok Southeast ore bodies represent satellite deposits generated by off-axis hydrothermal activities from vents aligned along a NW-SE trend with the Main Malusok zone. This alignment represents an ancient fissure that served as a pathway for the upwelling metalliferous hydrothermal fluids. In searching for lateral extensions of these VMS deposits, this NW-SE alignment should serve as a possible exploration guide.

Porphyry Cu–Au mineralisation associated with a multi-phase intrusion, and related replacement fronts in limestones in an island arc setting near the Gümüşhane village (Artvin) in the Eastern Black Sea Province (Turkey)

The Gümüşhane area near Artvin is highly characteristic due to a significant hydrothermal alteration zone genetically associated with a microdiorite stock and its late-stage derivatives in the form of porphyry plugs that intruded into all the pre-Middle Eocene lithologies. The porphyry intrusion is multi-stage, intermediate to felsic in composition, and divided into pre-ore feldspar porphyries and quartz–feldspar porphyries, syn-ore feldspar–amphibole porphyries, and post-ore feldspar porphyries. Sericitic alteration is dominant, but K-silicate alteration is also observed and is characterised mainly by secondary feldspars, biotites, quartz, anhydrite, magnetite and pyrite veinlets. The central part of the alteration and the porphyry system where syn-ore feldspar–amphibole porphyry outcrops coincides with intense quartz stock-working with anomalous but uneconomical Cu and Au values. In this zone, pyrite is ubiquitous and is accompanied by chalcopyrite and lesser sphalerite, sulphosalts, molybdenite, bornite and magnetite. Chemical analyses of surface and drill core samples show that overall Au and Cu values are around 0.5 ppm and 0.3%, respectively, and that they are in the ranges of 1–2 ppm and 0.3–0.4%, respectively, in the densest stock-work zones. Multi-phase intrusion of porphyries into Late Cretaceous limestone also caused replacement fronts along re-crystallised limestone and porphyry contacts. This type of mineralisation is enriched in Mn, Zn, Cu, Au and Ba, and contains on average 4.7% MnO, 3.2% FeO, 3.1% Zn, 0.95% Cu, 0.3% Pb, 200 ppb Au, 900 ppm Bi and 660 ppm Ba, present in Fe- and Mn-oxides, pyrite, chalcopyrite, sphalerite and lesser bornite, sulphosalts and gold. Supergene oxidation is well developed in these zones. Hydrothermal alteration mass change calculations reflect an intimate relationship between the two types of mineralisation. The lithologies near mineralised fronts are highly depleted in MnO and Zn, and the intensity of depletion is reduced away from the contact into the porphyry. The leached elements are added to the re-crystallised limestone block in which MnO and Zn show an 81-fold and 472-fold increase, respectively, over the least altered limestone. Au and Cu are enriched along the contact both in the porphyry and in the limestone, implying that they may have been derived either from other lithologies in the vicinity or the magma itself.

Quartz Crystal Microbalance (QCM) in High-Pressure Carbon Dioxide (CO2): Experimental Aspects of QCM Theory and CO2 Adsorption

The quartz crystal microbalance (QCM) technique has been developed into a powerful tool for the study of solid-fluid interfaces. This study focuses on the applications of QCM in high-pressure carbon dioxide (CO2) systems. Frequency responses of six QCM crystals with different electrode materials (silver or gold) and roughness values were determined in helium, nitrogen, and carbon dioxide at 35-40 degrees C and at elevated pressures up to 3200 psi. The goal is to experimentally examine the applicability of the traditional QCM theory in high-pressure systems and determine the adsorption of CO2 on the metal surfaces. A new QCM calculation approach was formulated to consider the surface roughness contribution to the frequency shift. It was found that the frequency-roughness correlation factor, Cr, in the new model was critical to the accurate calculation of mass changes on the crystal surface. Experiments and calculations demonstrated that the adsorption (or condensation) of gaseous and supercritical CO2 onto the silver and gold surfaces was as high as 3.6 microg cm(-2) at 40 degrees C when the CO2 densities are lower than 0.85 g cm(-3). The utilization of QCM crystals with different roughness in determining the adsorption of CO2 is also discussed.

Determination of the origin and mass change geochemistry during bauxitization process at the Hangam deposit, SW Iran

The Hangam bauxite deposit is located in the Firouzabad region in southwestern Iran. Structurally the deposit located in the Simply Folded Belt of the Zagros Mountains. The Hangam bauxite horizon, which lies between the Sarvak and the Ilam formations, is approximately 30 meters thick and covers an area of about 1 km2. According to stratigraphical and sedimentological data a sedimentary hiatus during Cenomanian-Turonian times has exposed the Sarvak Limestone to karst weathering and the layers of carbonate argillaceous debris (Basal Marly Limestone; Ferruginous Carbonate Marl; Red Marly Limestone; White Marly Limestone) accumulated on its surface, which was partly converted to bauxite (Pisolitic Bauxite, Yellow Bauxite and Red Bauxite). Twenty four samples were collected from eight layers of the deposit for laboratorys work. Microscopic studies of thin and polished-thin sections show pelitomorphic, fluidal, and pseudobrecciated textures, all poiting to an authigenic origin for the Hangam bauxite. This study uses the geochemistry of immobile elements to trace the precursor rock of the bauxite deposit and to calculate the mass changes that took place during weathering and bauxitization. Plots of chemical data and calculation of correlation coefficients show that Al and Ti were immobile during the bauxitization process and were used for mass change calculations. Mass changes were calculated from the concentration ratio of immobile elements for the different bauxite rocks and the Sarvak Limestone. As only one linear trend is evident in the Al-Ti binary diagram and the Sarvak Limestone coincides with this trend, we concluded that the source of the Hangam bauxite was the underlying argillaceous limestone (Sarvak Formation).