Interpretation Of Geochemical Data Research Articles

ANALISIS UNIVARIAT DAN MULTIVARIAT CONTO SEDIMEN SUNGAI DALAM PENENTUAN POTENSI MINERALISASI LOGAM DI HALMAHERA BAGIAN TIMUR, PROVINSI MALUKU UTARA

Penelitian geokimia dengan mengunakan metode analisis kandungan unsur dari conto endapan sungai aktif -80 mesh merupakan salah satu fase awal eksplorasi terutama untuk menemukan cebakan mineral logam. Halmahera bagian timur dengan tataan geologi yang kompleks dan berada dalam jalur metalogenik yang berpotensi membentuk cebakan logam, menghasilkan rona geokimia yang sangat bervariasi dan menarik. Data geokimia sedimen sungai aktif yang tertuang dalam bentuk peta sebaran unsur menyajikan informasi awal yang penting tentang indikasi mineralisasi untuk ditindaklanjuti ke tahap penelitian lebih rinci, khususnya mineralisasi nikel yang berasosiasi dengan litologi Komplek Ultrabasa.
 
 Penafsiran data geokimia di wilayah penelitian dengan pendekatan analisis statistik univariat dan multivariat yang terdiri dari unsur Cu, Pb, Zn, Co, Ni, Mn, Ag, Fe, Cr, dan Au, proses pengayaan unsur geokimia di lingkungan permukaan diperlihatkan oleh asosiasi spasial Co, Ni, Fe dan Mn, yaitu pengayaan unsur disebabkan pengikatan kimiawi (scavenging) oleh oksida Fe dan Mn. Berdasarkan kekerabatan unsur atau hubungan antar unsur diperoleh dua kelompok unsur yaitu ikatan unsur Cu-Pb-Zn-Ag-Cr dan Co-Ni-Mn-Fe-Au, akan tetapi tidak semua kelompok asosiasi unsur dapat dihubungkan dengan litologi di daerah penelitian.

Determination of the major geochemical processes of groundwater along the Cretaceous-Tertiary boundary of Trichinopoly, Tamilnadu, India

The hydrogeochemical variations in groundwater are mainly influenced by lithology, residence time of water in the aquifer matrix, and anthropogenic activities. This study was focused on the geochemical variations of groundwater in different lithological units (Archaean, Cretaceous, Tertiary, and Quaternary) by understanding the major factors governing the geochemical variations in each lithology. The 71 groundwater samples were collected from these rock types, namely, Archaean (14), Cretaceous (37), Tertiary (11), Quaternary (9). The collected samples were measured for major ions and they were used for preparation of standard geochemical plots and ionic ratios. Factor analysis and factor score were used to identify the major factors controlling the hydrochemistry and their spatial distribution in the study area. In addition, geochemical model, WATEQ 4F was used to determine the saturation condition of carbonate and sulphate minerals in the groundwater. Na–Cl and mixed Ca–Na–HCO3 were the dominant hydrochemical facies irrespective of lithological units. The overall interpretation of geochemical data revealed that leaching of secondary salts, weathering and ion exchange reaction along the groundwater flow path through various lithological units, and anthropogenic influence from domestic sewages and agricultural activities constitute the major geochemical processes in the study area. Hence, this study brings out the multiple hydrogeochemical process in the complex geological terrain along the Cretaceous-Tertiary boundary.

A Multivariate Geochemical Investigation of Borehole Samples for Gold Deposits Exploration

The aim of this paper is to carry out a geochemical multivariate analysis on Qolqola gold deposit which is located in Kordestan province of Iran. The analysis and interpretation of geochemical data was carried out based on the results of 543 drilling core samples analyzed for Cu, Pb, W, Mo, Ag, As, Bi, Hg and Au. The purpose of this paper is to use probability plot modeling method for anomaly separation and data classification. For this purpose, three sub-population from Au probability plot modeling was recognized and the thresholds obtained and labeled with the codes 0, 1, and 2 after modeling (code 0: Au 870 ppb as anomaly range). The rearranged data set was used to evaluate discriminant function method. The results were introduced Ag, Hg, Sb, W and Pb as variables related to the mineralization event. The stepwise method was reduced the important variables as Au, Ag, As, W and Bi. Base on the exploration information from the study area, variables such as Ag, As, Sb, Hg, W, Pb were considered as variables were affected by Au mineralization event.

Laser-Induced Breakdown Spectroscopy—An Emerging Analytical Tool for Mineral Exploration

The mineral exploration industry requires new methods and tools to address the challenges of declining mineral reserves and increasing discovery costs. Laser-induced breakdown spectroscopy (LIBS) represents an emerging geochemical tool for mineral exploration that can provide rapid, in situ, compositional analysis and high-resolution imaging in both laboratory and field and settings. We demonstrate through a review of previously published research and our new results how LIBS can be applied to qualitative element detection for geochemical fingerprinting, sample classification, and discrimination, as well as quantitative geochemical analysis, rock characterization by grain size analysis, and in situ geochemical imaging. LIBS can detect elements with low atomic number (i.e., light elements), some of which are important pathfinder elements for mineral exploration and/or are classified as critical commodities for emerging green technologies. LIBS data can be acquired in situ, facilitating the interpretation of geochemical data in a mineralogical context, which is important for unraveling the complex geological history of most ore systems. LIBS technology is available as a handheld analyzer, thus providing a field capability to acquire low-cost geochemical analyses in real time. As a consequence, LIBS has wide potential to be utilized in mineral exploration, prospect evaluation, and deposit exploitation quality control. LIBS is ideally suited for field exploration programs that would benefit from rapid chemical analysis under ambient environmental conditions.

Application of multi-element geochemistry in the weathered environment: Controls, considerations and implications for exploration

Understanding the mobility of individual elements in the oxidised environment is important for the accurate interpretation of geochemical data from regolith and weathered bedrock samples. In the we...

Paradox in bulk and molecular geochemical data and implications for hydrocarbon migration in the inter-salt lacustrine shale oil reservoir, Qianjiang Formation, Jianghan Basin, central China

This study analyzes the bulk and molecular geochemical data of 56 core samples of the Eocene Qianjiang Formation, a confined source rock unit embedded with salt intervals formed in a hypersaline lacustrine setting in central China. These source rocks within a single evaporative cycle collected from a recent shale oil exploration well are highly laminated, consisting of both intra- and inter-salt shales. Both organic pores and matrix pores serve as storage for hydrocarbon generated from kerogen within the source rock. Because the contrast in density between kerogen and oil, conversion of kerogen to oil inevitably leads to the increase in pore pressure and oil expulsion from kerogen within the same source rock unit. Impregnation of source rocks by expelled oils from nearby mature source rocks or from the organic-rich laminae within the same source rock units leads to anomalous Rock-Eval pyrolysis data, characterized by an abnormally high S1 peak, a high Production Index (PI), a suppressed Tmax and other anomalies. It is contradictory that both Rock-Eval pyrolysis data and sterane isomerization ratios of the studied inter-salt shale samples indicate strong impact of allochthonous hydrocarbons in the source rocks, whereas most aliphatic biomarker parameters obtained from the solvent extracts of these shales still provide useful information on the vertical variation in organic source input and depositional environment of the host rocks. This study provides insights into the bulk and molecular geochemical data interpretation, particularly in the inter-salt shale oil system evaluation in inferring the prevailing directions and pathways of diagenetic fluid movement and hydrocarbon migration.

Is seawater geochemical composition recorded in marine carbonate? Evidence from iron and manganese contents in Late Devonian carbonate rocks

Iron and manganese are the important redox-sensitive elements in the ocean. Previous studies have established a series of paleo-depositional redox proxies based on the form and content of iron in sedimentary rocks (e.g., degree of pyritization, FeHR/FeT, Fe/Al). These proxies were developed and applied on siliciclastic-rich marine sediments. Although marine carbonate rocks are generally considered to preserve the geochemical signals of ancient seawater, neither Fe nor Mn content in marine carbonate rocks (Fecarb, Mncarb) has been independently used as a proxy to quantify environmental cues in paleo-oceans. Both Fe and Mn are insoluble in oxic conditions (Fe2O3, Fe(OH)3, MnO2), while their reduced forms (Fe2+ and Mn2+) are soluble. Therefore, oxic seawater should have low concentrations of dissolved Fe2+ and Mn2+, and accordingly carbonate rocks precipitated from oxic seawater should have low Fecarb and Mncarb, and vice versa. To evaluate whether Fecarb and Mncarb can be used to quantify oxygen fugacity in seawater, we measured Fecarb and Mncarb of Upper Devonian marine carbonate rocks collected from nine sections in South China. Fecarb of intraplatform basin samples was significantly higher than that of shelf samples, while shelf and basin samples had comparable Mncarb. The modeling result indicates that the dramatic difference in Fecarb cannot be explained by variation in oxygen fugacity between the shelf and basin seawater. Instead, both Fecarb and Mncarb appear to be more sensitive to benthic flux from sediment porewater that is enriched in Fe2+ and Mn2+. Porewater Fe2+ and Mn2+ derive from bacterial iron and manganese reduction; flux was controlled by sedimentation rate and the depth of the Fe(Mn) reduction zone in sediments, the latter of which is determined by oxygen fugacity at the water–sediment interface. Thus, high Fecarb of the basin samples might be attributed to low sedimentation rate and/or low oxygen fugacity at the seafloor. However, invariant Mncarb of the shelf and basin samples might be the consequence of complete reduction of Mn in sediments. Our study indicates that marine carbonate rocks may not necessarily record seawater composition, particularly for benthic carbonate rocks. The influence of benthic flux might cause carbonate rocks’ geochemical signals to deviate significantly from seawater values. Our study suggests that interpretation of geochemical data from carbonate rocks, including carbonate carbon isotopes, should consider the process of carbonate formation.

Strontium (87Sr/86Sr) isotopes: A tracer for geochemical processes in mineralogically-complex mine wastes

Interpretation of geochemical data based primarily on elemental concentrations often lead to ambiguous results due to multiple potential sources including mineral weathering, atmospheric input, biological cycling, mineral precipitation and exchange processes. The 87Sr/86Sr ratio is however not fractionated by these processes. In this study, Sr isotope (87Sr/86Sr) ratios have been coupled with chemical data of Sr and Rb-bearing minerals, tailings and leachates (water-soluble) to gain insight into the geochemical processes occurring within the Yxsjöberg Cu-W mine tailings, Sweden. The tailings have been exposed to oxidizing conditions resulting in three geochemical zones namely (i) oxidized, (ii) transition and (iii) unoxidized zones. Leachates from the oxidized zone are acidic (pH = 3.6–4.5) and contain elevated concentrations of metals (e.g. Fe, Cu and Zn) and SO4. The low pH has also led to subsequent weathering of most silicates, releasing Al, Ca, Mg and Na into solution. The 87Sr/86Sr ratio in the tailings ranges from 0.84787 to 1.26640 in the oxidized zone, 0.92660–1.06788 in the transition zone, whilst the unoxidized zone has values between 0.76452 and 1.05169. For the leachates, the 87Sr/86Sr ratio ranges from 2.44479 to 5.87552 in the oxidized zone, 1.37404–1.68844 in the transition zone and 1.03697–2.16340 in the unoxidized zone. Mixing (between mineral weathering and atmospheric sources) was identified as the major process regulating the Sr composition of the tailings and leachates. The highly radiogenic signatures of the leachates in the oxidized zone suggests weathering of biotite, K-feldspar and muscovite. Despite the very radiogenic signatures in the oxidized zone, increments in Ca/K ratios, Be, Ce, Tl, Al, Fe and SO4 concentrations in the water-soluble phase were recorded in its lower parts which suggests the dissolution of amphibole, pyroxene, plagioclase, fluorite, gypsum, Al and Fe –(oxy) hydroxides as well as cation exchange by clay minerals. Presence of clay minerals has led to the partial retainment of radiogenic 87Sr/86Sr resulting in increased 87Sr/86Sr in the solid tailings material at these depths. The 87Sr/86Sr ratios of the water-soluble phase in the transition zone is similar to that of helvine and could indicate its dissolution. In the upper part of the unoxidized zone, the 87Sr/86Sr ratios and trends of Be, Ca, SO4, Tl and Zn in the water-soluble phase suggest the dissolution of gypsum which precipitated from a leachate with the isotopic signature of helvine. In the lower part of the unoxidized zone, elevated concentrations of W were recorded suggesting scheelite weathering. But the 87Sr/86Sr ratios are higher than that expected from dissolution of scheelite and indicates additional processes. Possible sources include biotite weathering and groundwater. This study reveals that when interpreting geochemical processes in mine waste environments, 87Sr/86Sr should be considered in addition to chemical constituents, as this isotopic tracer offers better insights into discriminating between different solute sources.

Major and trace elements in meimechites – rarely occurring volcanic rocks: developing optimal analytical strategy

The determination of the chemical composition of meimechites – which are unique and rarely occurring ultra-high MgO igneous rocks – can be complicated due to their porphyric structure, the presence of acid-insoluble minerals, and wide variation of major and trace element contents. In the present study the optimal analytical strategy based on a combination of X-ray fluorescence (XRF) and inductively coupled plasma mass spectrometry (ICP-MS) methods was suggested for the determination of the elemental composition of meimechites. The preparation of glass beads using a lithium tetraborate and metaborate mixture proved to be suitable for the XRF determination of major oxides. A comparative study of the sample decomposition procedures for the determination of trace elements by ICP-MS clearly showed that fusion with lithium metaborate was the most appropriate sample preparation technique for complete digestion of meimechites. The open beaker HF-HNO 3 -HClO 4 acid digestion was insufficient because the results for Nb, Ta, V, Zr, Cr and Hf were underestimated by 20–80% compared to those determined using the fusion method due to the presence in the rock samples of acid-resistant accessory minerals. It is shown that using analytical data from acid digestion may lead to erroneous interpretation of geochemical data. Supplementary material: Comparing the results obtained by ‘wet chemistry’ and XRF methods; ICP-MS data for meimechite samples; ICP-MS analysis of reference materials are available at https://doi.org/10.6084/m9.figshare.c.4226786

Ultramafic–Mafic Assemblage of Plutonic Rocks and Hornblende Schists of Shirshov Rise, Bering Sea, and Stalemate Ridge, Northwest Pacific: Geodynamic Interpretations of Geochemical Data

The paper presents data on plutonic and metamorphic rocks dredged during Cruise 249 of the German R/V Sonne to the Stalemate Ridge, Northwest Pacific Ocean and the Shirshov Rise, western Bering Sea. Dredges in the northwestern sector of the Stalemate Ridge and central portion of the Shirshov Rise show that the plutonic and metamorphic rocks obtained here are amazingly similar. Our petrologic and geochemical data led us to view the rocks as members of a mafic–ultramafic assemblage typical of cumulate portions of ophiolite complexes and backarc spreading centers. The plutonic complexes of the Shirshov Rise and Stalemate Ridge show similarities not only in the petrography and mineralogy of their protoliths but also in the character of their metamorphic transformations. Plutonic rocks from both areas display mineralogical evidence of metamorphism within a broad temperature range: from the high-temperature amphibolite facies to the greenschist facies. Relations between the index mineral assemblages indicate that the metamorphic history of plutonic complexes in the Stalemate Ridge and Shirshov Rise proceeded along a retrograde path. Hornblende schists accompanying the plutonic rocks of the Stalemate Ridge and Shirshov Rise are petrographically close to foliated amphibolites in subophiolitic metamorphic aureoles. Within the framework of geodynamic interpretations of our results, it is realistic to suggest that the examined plutonic complexes were exhumed from subduction zones of various age.

Geochemistry of basaltic flows from a basalt ring structure of the Serra Geral formation at Água Vermelha dam, Triângulo Mineiro, Brazil: implications for the magmatic evolution of the Paraná-Etendeka Province

The Serra Geral Formation belongs to the Parana-Etendeka Magmatic Province (PEMP) and its geochemical and petrographic characteristics are not homogeneous. Many studies segment this group into six basaltic and two rhyolitic magma-types. It is believed that its extrusion occurred through crustal fissures in the Cretaceous, but some authors described the presence of conduits in the shape of basaltic ring structures (BRS) in the Agua Vermelha region in the North of the province. The BRS rocks, based on textures and structures, were divided into four groups—central flow, basal flow, main ring dyke and lava flow—with a very similar petrography, composed of plagioclase (labradorite-bytownite), clinopyroxene (augite) and oxide (titanomagnetite) with intergranular texture. The whole-rock analyses of the basal and lava flows allow classifying them as tholeiitic basalts of the Paranapanema magma-type. Geochemical data interpretation suggests an enriched magma source, with low degree of partial melting, high depth of melt generation and without significant crustal contamination. The BRS experienced fractional crystallization on shallow magma chamber, influenced by successive new injections from different parental magmas which would be responsible for the pulses of effusion and explosion. Thus, the singularities of the BRS of Agua Vermelha are important to comprehend the evolution of the PEMP.

Geochemical Exploration for Gold and Associated Elements in the Granite Rocks at Wadi Al Marsad, Southwest Jordan

This study aimed to conduct a geochemical exploration for gold (Au) and associated elements from the granitoids rocks, to an attempt to outline the areas of abnormal concentration of gold and other elements such as As, Sn, Zn, Cu, Pb, Bi, Li, Be, Y, Nb, La, Ce, Mo, Fe 2 O 3 and TiO 2 . The geochemical anomalies areas were identified by using rock and Heavy Mineral geochemical methods. A total of 57 rock geochemical samples were collected from the granite, pegmatite, rhyolite dyke, quartz veins and ultration zone from the study area; and 37 Heavy Mineral (HM) geochemical panned concentrate samples were collected from the hillside sediments along the main valley and tributary from 30 cm depth and then sieved to 2 from the Northern part of Wadi El Marsad. Geochemical exploration for the abnormal concentration of gold and associated elements are used to identified the geochemical anomalies areas. The geochemical samples were chemically analyzed for their element components using Inductively Coupled Plasma Atomic Emission Spectrometry method (ICP-AES) and graphite furnace Atomic Absorption Spectrometer (AAS) method was used for the analysis of gold.. The results of geochemical analysis indicated the presence of gold in the study area; this result was considered abnormal for rock samples, while the gold was associated with vein, pegmatite and quartz veins. The presence of HM in the samples served as good indicators of gold in the area due to the detritus of gold-traces bearing rocks in the area. The Pearson’s correlation coefficients for the rock geochemical samples shows strong positive correlation was recorded for Au with As (r = 0.72), Cu (r = 0.78), Bi (r = 0.76), Y (r = 0.97), Nb (r = 0.94) and Ce (r = 0.50), respectively. The positive correlations for these metals revealed that the hydrothermal alterations affects the association of the metals in ultration zone, quartz veins and pegmatite dyke. The combination of both rock and HM concentrate samples showed three anomalous areas of gold. The interpretation of geochemical data for multi-elements of the rock samples shortlisted six geochemical anomalous areas and high concentration of Fe 2 O 3 , TiO 2 , As, Sn, Zn, Cu, Pb, Bi, Li, Be, Y, Nb, La, Ce and Mo. The HM samples indicated mineral concentration in the sulfide vein and pegmatite dyke at the sampled points; these elements are usually associated with sulfide minerals.

Identification of mineralization pattern in high frequencies of geochemical data by using the new approach of DWT-PCA

summary The Dalli area has been introduced as copper–gold probably porphyry mineralized area in the central part of Iran. In this study, in order to determine the mineralization pattern, a new method based on coupling discrete wavelet transform (DWT) and principal component analysis (PCA) has been used. The surface geochemical data of 30 elements were transformed to position – scale domain using 2DWT and were decomposed to high and low frequencies in one level then PCA was performed on vertical and horizontal detail components separately. In the final, the elements of Au and Cu have been classified clearly using the combination of mineralization factors obtained of vertical and horizontal detail components. The results of this study demonstrate that the DWT – PCA combined approach is a modern method for geochemical data processing. Introduction In this paper, the position - scale domain of geochemical data, using 2dimensional discrete wavelet transform has been represented and analyzed on Cu–Au porphyry deposit in northern Dalli area and the results have been discussed. Wavelet analyses have led to very successful results in numerous scientific and engineering fields such as signal analysis and numerical applications. Methodology and Approaches WT is a tool for the analysis of signals. Wavelets are used as the basis functions for signal representation such as sines and cosines. In the DWT, detailed and approximation coefficients are obtained with the wavelet algorithm based on high-pass and low-pass filters. In this paper, a new method is proposed based on coupling Haar DWT and Principal component analysis (PCA) for mineralization elements forecasting applications. PCA is a multivariate statistical method for geo-information identification of geo-datasets. Results and Conclusions The wavelet coefficients of geochemical data in vertical and horizontal detail components have appropriate exploratory information. The results of this analysis on the Haar WT have desirably identified the mineralizing elements. Hence, the Haar wavelet is a suitable mother wavelet for interpretation of geochemical data. The surface information and the exploration drillings in the study area confirm the results of WT.

Integration of soil magnetometry and geochemistry for assessment of human health risk from metallurgical slag dumps

The main objective of the study was an assessment of the pollution level of agricultural land located close to dumps of industrial waste remaining after former Zn and Pb ore processing in Poland. The integrated geophysical-geochemical methods were applied for assessment of soil quality with respect to trace element pollution. Additionally, human health risk induced by the contaminated arable soil and dusting slag heap was estimated. The investigations pointed out that soils in the vicinity of the metallurgical slag dump in Piekary were heavily polluted. Spatial distribution of magnetic susceptibility corresponding well with distribution of the content of potentially toxic elements indicated the local “pollution hotspots.” Proper geophysical and geochemical data interpretation supported by statistical factor analysis enabled identification of three different sources of pollution including metallurgical slug dump as a main source, but also traffic pollution influencing the area located along the busy road and relatively strong influence of the geochemical background. Computed health hazard index revealed no adverse health effect to the farmers cultivating arable soil, but in the direct vicinity of dusting, slag dump health risk occurred, caused mostly by very toxic elements as As and Tl. In the future, investigation should be focused on contribution of different sources to the heavy metal pollution in soil-crop system in this area. It should be highlighted that a site-specific approach should be taken in order to redevelop this kind of area in order to reduce ecological and human health threat. The study proved the integrated two-stage geophysical-geochemical method to be a feasible, reliable, and cost-effective tool for identification of the extent of soil pollution and areas at risk.

A geochemical and geophysical reappraisal to the significance of the recent unrest at Campi Flegrei caldera (Southern Italy)

AbstractVolcanic unrest at calderas involves complex interaction between magma, hydrothermal fluids, and crustal stress and strain. Campi Flegrei caldera (CFc), located in the Naples (Italy) area and characterized by the highest volcanic risk on Earth for the extreme urbanization, undergoes unrest phenomena involving several meters of uplift and intense shallow microseismicity since several decades. Despite unrest episodes display in the last decade only moderate ground deformation and seismicity, current interpretations of geochemical data point to a highly pressurized hydrothermal system. We show that at CFc, the usual assumption of vapor‐liquid coexistence in the fumarole plumes leads to largely overestimated hydrothermal pressures and, accordingly, interpretations of elevated unrest. By relaxing unconstrained geochemical assumptions, we infer an alternative model yielding better agreement between geophysical and geochemical observations. The model reconciles discrepancies between what observed (1) for two decades since the 1982–1984 large unrest, when shallow magma was supplying heat and fluids to the hydrothermal system, and (2) in the last decade. Compared to the 1980's unrest, the post‐2005 phenomena are characterized by much lower aquifers overpressure and magmatic involvement, as indicated by geophysical data and despite large changes in geochemical indicators. Our interpretation points out a model in which shallow sills, intruded during 1969–1984, have completely cooled, so that fumarole emissions are affected now by deeper, CO2‐richer, magmatic gases producing the modest heating and overpressure of the hydrothermal system. Our results have important implications on the short‐term eruption hazard assessment and on the best strategies for monitoring and interpreting geochemical data.

Ferroan Dolomitization by Seawater Interaction with Mafic Igneous Dikes and Carbonate Host Rock at the Latemar Platform, Dolomites, Italy: Numerical Modeling of Spatial, Temporal, and Temperature Data

Numerous publications address the petrogenesis of the partially dolomitized Latemar carbonate platform, Italy. A common factor is interpretation of geochemical data in terms of heating via regional igneous activity that provided kinetically favorable conditions for replacement dolomitization. New field, petrographic, XRD, and geochemical data demonstrate a spatial, temporal, and geochemical link between replacement dolomite and local mafic igneous dikes that pervasively intrude the platform. Dikes are dominated by strongly altered plagioclase and clinopyroxene. Significantly, where ferroan dolomite is present, it borders dikes. We hypothesize that seawater interacted with mafic minerals, causing Fe enrichment in the fluid that subsequently participated in dolomitization. This hypothesis was tested numerically through thermodynamic (MELTS, Arxim-GEM) and reactive flow (Arxim-LMA) simulations. Results confirm that seawater becomes Fe-enriched during interaction with clinopyroxene (diopside-hedenbergite) and plagioclase (anorthite-albite-orthoclase) solid solutions. Reaction of modified seawater with limestone causes ferroan and nonferroan replacement dolomitization. Dolomite quantities are strongly influenced by temperature. At 40 to 80°C, ferroan dolomite proportions decrease with increasing temperature, indicating that Latemar dolomitization likely occurred at lower temperatures. This relationship between igneous dikes and dolomitization may have general significance due to the widespread association of carbonates with rifting-related igneous environments.

Comparison of Mineralization Pattern of Geochemical Data in Spatial and Position-scale Domain Using New DWT- PCA Approach

Abstract: In the current research to determine the mineralization pattern and discuss the mineralization components, the information of position - scale domain of geochemical data has been analyzed. A new method is proposed based on coupling discrete wavelet transforms (DWT) and principal component analysis (PCA) for mineralization elements forecasting applications. The results of this study indicate the potential of DWT – PCA method for geochemical data processing. Wavelet transform (WT), as a multi-spectral analysis method, can decompose the spatial and temporal signals into different frequencies. The features of mineralization can be identified using the position - scale domain of geochemical data that may not be achievable in spatial domain. The geochemical data from the Dalli region have been processed in the spatial domain using PCA. The surface geochemical data of 30 elements have been transformed to position – scale domain using two-dimensional discrete wavelet transform (2DDWT). Wavelet functions (WFs) of Haar, Coiflet2, Biorthogonal3.3 and Symlet7 have been applied separately to decompose the geochemical data to high and low frequencies in one level. To obtain more accurate and complete information of mineralization, a new index has been presented based on wavelet coefficients. Based on this new index, significant results have been obtained by using PCA of the index. The coefficients distribution map (CDM) as a new exploratory criterion has been generated based on 2DDWT to show the geochemical distribution map (GDM). Finally, the results of WT have been compared with the results of spatial domain and the best method of wavelet for interpretation of geochemical data has been introduced. The results of geochemical data analysis by DWT – PCA approach have been confirmed by the exploratory drillings in the study area.

Noble gas fractionation during subsurface gas migration

Environmental monitoring of shale gas production and geological carbon dioxide (CO2) storage requires identification of subsurface gas sources. Noble gases provide a powerful tool to distinguish different sources if the modifications of the gas composition during transport can be accounted for. Despite the recognition of compositional changes due to gas migration in the subsurface, the interpretation of geochemical data relies largely on zero-dimensional mixing and fractionation models. Here we present two-phase flow column experiments that demonstrate these changes. Water containing a dissolved noble gas is displaced by gas comprised of CO2 and argon. We observe a characteristic pattern of initial co-enrichment of noble gases from both phases in banks at the gas front, followed by a depletion of the dissolved noble gas. The enrichment of the co-injected noble gas is due to the dissolution of the more soluble major gas component, while the enrichment of the dissolved noble gas is due to stripping from the groundwater. These processes amount to chromatographic separations that occur during two-phase flow and can be predicted by the theory of gas injection. This theory provides a mechanistic basis for noble gas fractionation during gas migration and improves our ability to identify subsurface gas sources after post-genetic modification. Finally, we show that compositional changes due to two-phase flow can qualitatively explain the spatial compositional trends observed within the Bravo Dome natural CO2 reservoir and some regional compositional trends observed in drinking water wells overlying the Marcellus and Barnett shale regions. In both cases, only the migration of a gas with constant source composition is required, rather than multi-stage mixing and fractionation models previously proposed.

The Chahnaly Low-Sulfidation Epithermal Gold Deposit, Western Makran Volcanic Arc, Southeast Iran

The Chahnaly low-sulfidation epithermal Au deposit and nearby Au prospects are located northwest of the intermittently active Bazman stratovolcano on the western end of the Makran volcanic arc, which formed as the result of subduction of the remnant Neo-Tethyan oceanic crust beneath the Lut block. The arc hosts the Siah Jangal epithermal and Kharestan porphyry prospects, near Taftan volcano, as well as the Saindak Cu-Au porphyry deposit and world-class Reko Diq Cu-Au porphyry deposit, near Koh-i-Sultan volcano to the east-northeast in Pakistan. The host rocks for the Chahnaly deposit include early Miocene andesite and andesitic volcaniclastic rocks that are intruded by younger dacitic domes. Unaltered late Miocene dacitic ignimbrites overlie these rocks. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb zircon geochronology data yield ages between 21.8 and 9.9 Ma for the acidic-intermediate regional volcanism. The most recent volcanic activity of the Bazman stratovolcano involved extrusion of an olivine basalt during Pliocene to Quaternary times. Interpretation of geochemical data indicate that the volcanic rocks are synsubduction and calc-alkaline to subalkaline. The lack of a significant negative Eu anomaly, a listric-shaped rare earth element pattern, and moderate La/Yb ratios of host suites indicate a high water content of the source magma. Gold and electrum are temporally and spatially related to a series of structurally controlled, 030°-trending, subvertical hydrothermal breccias with chalcedony-adularia that cut porphyritic andesite and andesitic volcaniclastic rocks. Gold is associated with pyrite, a siliceous matrix of hydrothermal breccia, and previously formed vein clasts, as well as with iron oxides and hydroxides in oxidized zones. Rare silver minerals include Ag-bearing electrum and naumannite, iodargyrite, an unnamed silver diiodide, and hessite. Hydrothermal alteration is generally well developed surrounding the ore-bearing hydrothermal breccia. The main types of alteration in the area include an inner ~0.5- to 20-m-thick gold-bearing hydrothermal breccia composed of quartz-chalcedonyadularia-illite-pyrite, a ~5- to 50-m-thick zone of quartz, chalcedony, pyrite, illitic phengite, phengite, illitic muscovite, illite, illitic paragonite, paragonite, muscovite, montmorillonite and, rarely, siderite, and a 30- to 70-m outer propylitic zone of Fe-Mg chlorite, calcite, ankerite, dolomite, epidote, palygorskite, and pyrite. The Chahnaly Au deposit formed during the early stages of magmatism. LA-ICP-MS zircon U-Pb geochronology of host andesite and 40Ar/39Ar dating of two samples of gold-associated adularia show that the ore-stage adularia (19.83 ± 0.10 and 19.2 ± 0.5 Ma) is younger, by as much as 1.5 million years, than the volcanic host rock (20.32 ± 0.4 Ma). Therefore, either hydrothermal activity continued well after volcanism or a second magmatic event rejuvenated hydrothermal activity. This second magmatic event may be related to eruption of porphyritic andesite at ~20.32 ± 0.40 Ma, which is within error of ~19.83 ± 0.10 Ma adularia. The new LA-ICP-MS zircon U-Pb host rock and vein adularia 40Ar/39Ar ages suggest that early Miocene magmatism and mineralization in the Bazman area is of a similar age to that of the Saindak porphyry and Tanjeel porphyry center of the giant Reko Diq deposit. This confirms the existence of early Miocene arc magmatism and mineralization along the Iranian part of the Makran volcanic arc. Ore, alteration mineralogy, and alteration patterns indicate that the Chahnaly deposit is a typical low-sulfidation epithermal Au deposit, located in a poorly explored part of the Makran volcanic arc in Iran.

The Messinian marine to nonmarine gypsums of Jumilla (Northern Betic Cordillera, SE Spain): Isotopic and Sr concentration constraints on the origin of parent brines

The origin of the Messinian Hoya de la Sima (HS) gypsum (Betic foreland) is constrained using 87Sr/86Sr, δ34S, Sr concentration, and petrographic data. The Lower and Middle HS units consist of subaqueous vertically-aligned and stromatolitic selenites, the latter containing unusual microbial depositional textures. The Upper Unit consists of very-shallow-water bioturbated lenticular gypsum with Paracamelus ichnites. 87Sr/86Sr and δ34S indicate precipitation from predominantly marine waters, with upward increasing continental influence. Mixing models between Messinian seawater and continental water that dissolved Triassic evaporites show that the percentages of seawater required to explain the measured 87Sr/86Sr are analogous to the percentages obtained using δ34S, supporting precipitation from such mixtures. 87Sr/86Sr and δ34S of Lower HS selenites resemble those of the Primary Lower Gypsum (PLG) of the Messinian Salinity Crisis (MSC), in both cases indicating precipitation from seawater–continental water mixtures in which most Sr and SO4 were supplied by Messinian seawater. In the Lower HS selenites, Sr concentrations indicate contributing continental waters with Sr/Ca ratios similar to seawater. However, Sr concentrations of PLG selenites from other Betic basins (Bajo Segura, Sorbas indicate parent waters with Sr/Ca ratios lower than seawater. If the Sr contents of the betic PLG selenites are representative, it is unlikely that the Lower HS selenites represent the PLG. However, we cannot completely discard that option since different LPG subbasins could have had variable Sr/Ca. The HS gypsums formed coevally to diapirism of Triassic evaporites, in a restricted lagoonal basin developed during or slightly after a phase of strike-slip faulting in the Betic Cordillera. More general implications of this work are that Sr concentrations, combined with 87Sr/86Sr and δ34S data, provide key constraints on the origin of parent brines, and using Sr concentrations as paleosalinity proxy in gypsum precipitated from seawater–continental water mixtures is inconclusive because they largely depend on the initial Sr/Ca ratio of the brine. This study also illustrates that the electron microprobe is ideal to obtain reliable, spatially-resolved, Sr concentration data in selenitic gypsum. These data, in combination with fluorescence petrography, provide valuable criteria to discriminate primary depositional from diagenetic gypsum, a critical step in the interpretation of geochemical data.