Detailed Geochemical Survey Research Articles

Machine learning and data augmentation approach for identification of rare earth element potential in Indiana Coals, USA

Rare earth elements and yttrium (REYs) are critical elements and valuable commodities due to their limited availability and high demand in a wide range of applications and especially in high-technology products. The increased demand and geopolitical pressures motivate the search for alternative sources of REYs, and coal, coal waste, and coal ash are considered as new sources for these critical elements. This research evaluates the REY potential of coals from Indiana (USA). However, although coal data revealed REY potential, it suffered from sparse samples with complete REY measurements. Therefore, we explore the applicability of machine learning (ML) models and data augmentation techniques to demonstrate their applicability to evaluate REY potential in Indiana, and other areas in coal basins, using selected coal parameters (Al2O3, Fe2O3, C, Ash, S, P, Mo, Zn, and As contents) as covariates (indicators). Due to the relatively small sample size with complete REY data in the Indiana Coal Database, two data augmentation techniques (Random Over-Sampling Examples and Synthetic Minority Over-Sampling Technique) were used. Four machine learning algorithms (linear discriminate analysis, support vector machine, random forest, and artificial neural networks) were applied for modeling REY potential as a classification problem. The results show that application of Synthetic Minority Over-Sampling Technique prior to development of the support vector machine (SVM) models generated the best REY classification with an accuracy of 95%. The encouraging results based on Indiana coal data may suggest that a similar approach can be used for other coal basins for screening the locations with REY potential. Those locations then can be targeted for more detailed geochemical surveys to identify most promising areas and evaluate overall REY resources.

Application of the fine-grained soil prospecting method in a loess-covered area of central China

Loess-covered landscapes occupy a large area of the globe and have substantially high potential for mineral exploration; however, as mineral information is obscured by loess cover, suitable prospecting techniques need to be applied. The fine-grained soil prospecting method—a deep-penetrating geochemical technology that can be used to identify concealed deposits—has been proven effective in some cases. In this study, we applied this method for mineral exploration in the loess-covered Luoning Basin in Central China. Our results revealed strong geochemical anomalies (e.g., Au, Ag, Pb, Zn, and Cu) over related and concealed ore deposits. Furthermore, a regional geochemical survey in the Luoning Basin revealed the spatial distribution and suites of elements that were consistent with the mineralization type. Moreover, higher geochemical anomalies of Au, Ag, Pb, and Zn were spatially related to an Au ore deposit and Ag–Pb–Zn polymetallic deposit, respectively. The results of a detailed geochemical survey in the Zhonghedi Ag–Pb–Zn polymetallic deposit further revealed that the distribution of surface element anomalies was associated with tectonic fractures throughout the exploration region, which are closely related to the distribution of orebodies. These results imply that the fine-grained soil prospecting method is suitable for anomaly delineation during detailed geochemical surveys as well as regional-scale surveys. Based on our results, we suggest that geochemical anomalies in the loess-covered surface in our study area are presumably the result of geogas dispersion processes; we provide a schematic model explaining how ore-forming and associated materials are brought to the surface by geogas flowing upwards along faults and fractures and, ultimately, accumulating in fine-grained loess soils. Overall, our research demonstrates that fine-grained soil prospecting can effectively aid the search for concealed mineral deposits in loess-covered landscapes.

Effects of montane watershed development on vulnerability of domestic groundwater supply during drought

Climate change is expected to reduce recharge to montane aquifers in the western United States, but it is unclear how this will impact groundwater resources in watersheds where intensive surface-water development has disrupted the natural hydrologic regime. To better understand sources of recharge and associated vulnerabilities of groundwater supply in this setting, we made a detailed geochemical survey of domestic wells finished in fractured bedrock throughout the Yuba and Bear River watersheds (Sierra Nevada foothills, northern California) during historic drought (2015–2016). Stable isotopes of water and noble gas recharge temperatures closely tracked atmospheric lapse rates across a broad elevation gradient (100–2000 m), indicating groundwater inputs are dominated by local precipitation that rapidly recharges fractured bedrock during the winter wet-season. However, nearly one-quarter of wells had water isotopes that were fractionated by evaporation and warm recharge temperatures, indicative of mixing with dry-season recharge by surface water. Monte Carlo mixing models suggest evaporation-impacted groundwater samples are mixtures of local rain with an average of 28% ± 13% from diverted surface water that can recharge bedrock aquifers during the dry-season by either irrigation return flow or seepage from extensive distribution infrastructure. Wells that received recharge subsidies from diverted surface water had elevated levels of nitrate and coliform bacteria compared to those replenished exclusively by local precipitation, which are more vulnerable to supply shortage during drought. It is important to consider the impacts of increased surface-water development on the quantity and quality of groundwater recharge in rapidly developing montane watersheds.

Background Variation and Threshold Values for Cadmium Concentration in Terra Rossa Soil from Dalmatia, Croatia

The objectives of this study were to (i) establish the background variation and determine a threshold values for aqua regia soluble cadmium (Cd) in Terra Rossa soil at the local scale (Dalmatia, Croatia), (ii) check for possible soil Cd enrichment comparing its concentration at two different depths, and (iii) compare the threshold values for Cd calculated applying different statistical techniques with soil guideline values (SGV) as defined in Croatia and other national systems in Europe. The four statistical methods (the mean ± 2 standard deviations [mean ± 2SD], the median ± 2 median absolute deviations [median ± 2MAD], the (upper) Tukey inner fence (TIF), and the percentile-based approach) were used to establish the threshold values for Cd and identify samples with high Cd concentrations deviating from the background variation in a studied dataset. Overall, 74 samples from the A horizon of Terra Rossa soil were analyzed for aqua regia soluble Cd concentration (CdA); major soil properties—pH, CaCO3, soil organic carbon (SOC) content, P2O5, K2O, and particle-size distribution—were also determined in these samples. The underlying cambic B horizon was analyzed only for Cd concentration (CdB) The median CdA and CdB values of 1.84 and 1.70 mg kg–1, respectively as well as the maximum value of 8.53 mg kg–1 in the A horizon and 7.56 mg kg–1 in the B horizon obtained in this study attested to anomalously high Cd concentrations. The median CdA/CdB ratio was close to unity (1.07) indicating very low Cd enrichment in the A horizon. The [median ± 2MAD] method achieved the lowest threshold Cd value of 4.68 mg kg–1 and, consequently, a maximum number of outliers; it was followed by the classical [mean ± 2SD] method (5.01 mg kg–1), the Q95th percentile (5.29 mg kg–1), the Q98th percentile (5.64 mg kg–1), and the TIF method with the highest threshold value of 6.93 mg kg–1. All specified threshold values for Cd concentration repeatedly exceeded the maximum admissible concentrations (MACv) for agricultural land as defined in soil guideline values developed in Croatia and in several countries of the European Union. These findings indicate that more attention should be paid to the unusually high Cd concentrations in Terra Rossa soils originating from the natural sources; a more detailed geochemical survey of these soils should be performed in the future.

Urban soil geochemistry of an intensively developing Siberian city: A case study of Tyumen, Russia

Complex studies of soil cover within the urbanized areas represent one of the main research directions in environmental geochemistry. Urban soil geochemistry depends on a combination of natural and urbanization factors unique to each urban environment. Although Tyumen, in Western Siberia, is an intensively developing urban city, a detailed geochemical survey of its soils has never been performed. In this study, we conducted a systematic geochemical soil survey across the urbanized area of Tyumen, Russian Federation. Surface soil samples (0–10 cm) were collected from 241 sampling sites: 1 × 1 km regular grid for highly urbanized areas, and 4 × 4 km grid for peripheral parts of the city. The contents of V, Cr, Co, Ni, Cu, Zn, As, Sr, and Pb were determined using XRF analysis. Data were interpreted using GIS and multivariate statistical analyses, including hierarchical cluster analysis and principal components analysis. The results showed a non-uniform spatial distribution of individual metals, associated with natural soil-lithological conditions and urban environment characteristics. Our data showed that variation in soil element content was origin dependent: V, Cr, and Co contents were related to their natural origin; As and Pb to their anthropogenic origin; and Ni, Cu, and Zn to their mixed origin. Elevated V, Cr, Co, Ni, Cu, and Zn contents correlated with proximity to motorway networks and machinery. Strong As and Pb anomalies were associated with the activity of battery enterprises. The spatial distribution of Sr was significantly different from other studied elements — anomalous content of this metal was confined to hydromorphic boggy landscapes of the city's northern part. In general, Tyumen territory was slightly polluted with metals. Zn and Pb contents were slightly lower than in most cities with similar population levels, while those of V and Co were higher. Other metal contents were comparable to those in large cities, with a long history of industrial development. Elevated Cr, Ni, Zn, Cu, As, Pb, and Co contents were observed in areas that developed during mid last century.

Chemical and isotopic signatures of hot springs from east-central Sonora State, Mexico: a new prospection survey of promissory low-to-medium temperature geothermal systems

A promissory low-to-medium temperature geothermal system located in Sonora (Mexico) has been studied. In the present work, a detailed geochemical survey was carried out to understand the hydrogeochemical signatures of hot spring waters. A field work campaign was conducted for collecting water samples from twelve hot springs placed in four major zones (NW, NE, C, and S). The collected samples were analysed by chemical and isotopic methods for determining their chemical (major and trace elements) and isotopic (18O/16O and D/H) compositions. Using geochemometric analyses of the fluid composition and fractionation, depletion and enrichment processes exhibited by major and trace elements were analysed.
 Hydrogeochemical classification was used to indicate the presence of sodium-sulphate (Na-SO4) waters in the North (NW and NE) and South hydrothermal zones; whereas calcium-magnesium-bicarbonate (Ca-Mg-HCO3) waters were identified for the Central zone. Some hot spring waters located in the NE zone were also typified as sodium-bicarbonate (Na-HCO3). In relation to the isotopic signatures of 18O/16O and D/H, four water samples from NE and C zones lie near to the global meteoric water line; whereas the remaining eight samples showed a shift for both oxygen and deuterium isotopes. A mixing line with a small shift of δ18O was identified and used as a proxy to discriminate waters with different isotopic signatures.
 After applying a geochemometric outliers detection/rejection and an iterative ANOVA statistical test, the mean temperature inferred from the most reliable solute geothermometers was 149±40 °C, which suggests to be considered as the minimum value of the reservoir temperature. As most of the hot spring waters fall outside of the full equilibrium curve, the original reservoir conditions were corrected by using a mixing conductive model, which predicted a deep equilibrium temperature of 210±11 °C. As this temperature is considerably higher than the mean temperature inferred from the geothermometers, it was suggested as an optimistic maximum reservoir temperature of the Sonora geothermal system.
 Using 150 °C and 200 °C as rounded-off reservoir temperatures (or min-max estimates), geochemical equilibria modelling based on fluid-mineral stability diagrams was carried out. An equilibrium process among local hydrothermal waters and albite-potassium feldespar and muscovite-prehnite-laumontite mineral assemblages was found. These minerals were proposed as representative mineral assemblages of low-grade metamorphism, which seems to indicate that the geothermal fluid equilibria were probably reached within the intermediate to acidic volcanic rocks from the Tarahumara Formation.

Using halogens (Cl, Br, I) to understand the hydrogeochemical evolution of drought-derived saline porewater beneath a prairie wetland

Numerous closed-basin prairie wetlands throughout the Prairie Pothole Region (PPR) of North America maintain moderate surface pond salinities (total dissolved solids [TDS] from 1 to 10gL−1) under semiarid climate by accumulation of gypsum and saline lenses of sulfate-rich porewater (TDS>10gL−1) in wetland sediments during droughts. In order to understand the hydrogeochemical origin and composition of these saline porewaters, we made a detailed geochemical survey of Cl−, SO42−, Br, and I in the porewater, pondwater, and upland groundwater of a typical closed-basin prairie wetland (P1 in the Cottonwood Lake study area, North Dakota). Concentrations of Cl− ranged up to 5.9mM in the saline porewaters, and was strongly correlated with SO42− and Br (Pearson's r>0.7, p<0.05; concentrations ranging up to 131mM and 39μM, respectively) due to the conservative effects of surface water evaporation. In contrast, total dissolved I was not significantly correlated with Cl− (Pearson's r=0.18, p=0.273) and was concentrated in porewaters located above the saline lenses with a peak concentration of 4.1μM beneath the center of the wetland— the highest value for dissolved I ever measured in a terrestrial aquatic system and an order of magnitude above that of seawater. We hypothesize that chromatographic separation between more mobile anions (Cl−, SO42−, Br−) and I occurs during droughts when wetland ponds dry and sedimentary iodide (I−) oxidizes to its less-mobile form, iodate (IO3−). Understanding the origin and geochemical composition of porewater salinity that develops beneath prairie wetlands during drought can help to fingerprint sources of salinity to wetland ponds during wet climate and elucidate halogen systematics in saline and organic-rich subsurface environments associated with hydrocarbon generation.

Pollution of near-surface zone in the vicinity of gas wells

The results of a surface geochemical and geoelectrical survey carried on around gas wells drilled in the vicinity of Sucha Beskidzka town (Western Carpathians, southern Poland) are presented. The study area includes three wells located 8–10m apart, from which one has already been plugged and abandoned (P&A). In this area 46 soil gas samples were collected from a depth of 1.2m below the surface. Samples were analyzed for concentrations of light hydrocarbons and carbon dioxide. Mean methane concentration in soil gas reached almost 2.7vol.%, with a maximum value exceeded 26vol.%. Mean concentration of total alkanes C2–C5 was 0.02vol.%, with a maximum concentration close to 0.75vol.%. Mean concentration of total alkenes C2–C4 was 0.00013vol.%, with a maximum concentration close to 0.0056vol.%. Mean concentration of carbon dioxide reached 2.3vol.%, with a maximum concentration of 7.7vol.%. Relationships between these measured hydrocarbons and isotopic composition of ethane indicate deep source gases. A detailed geochemical survey was completed concurrently with a geoelectrical survey using electric resistivity tomography (ERT) and DC resistivity, pole–dipole sounding. Results showed that the distribution of hydrocarbon concentrations in soil gas correlates well with the electrical resistivity of near-surface rocks. Zones of lowered resistivity (caused by increased amounts of clays) correspond to the zones of lower hydrocarbon concentrations, whereas high hydrocarbon concentrations coincide with the zones of increased resistivity. Simultaneously, zones of much lower resistivity were identified, suggesting the presence of groundwater possibly containing increased TDS.Results of this study show that soil gas surveys conducted in the vicinity of oil wells can be used to determine the presence of anomalous concentrations of light hydrocarbons and carbon dioxide. Measured concentrations of methane can exceed the explosive limit (5%), which could create hazardous conditions. In addition, groundwater can be polluted with brine seeping from leaking well casings. These results suggest that pollution of the near-surface soil/aquatic environment associated with leakage from improperly closed oil and gas wells can cause a disturbance of near-surface geological formations associated with oil field operations.

Distribution of Heavy Metals around the Dashkasan Au Mine

The aim of the study is to determine the major source and extent of metal pollution in the vicinity of Dashkasan gold mine. Dashkasan mine has resulted in extensive contamination of soils by Arsenic (As) and potentially toxic ore-related elements including Mercury (Hg), Antimony (Sb) and Cadmium (Cd). Soils samples were collected and analyzed for As, Cd, Hg, Pb and Sb. The concentration of each heavy metal is controlled by different parameters (soil pH, iron and aluminum oxide content, clay content, organic matter and cation exchange capacity). The maximum content in the soils were 485, 3.2, 100, 2710 and 640 mg/kg for As, Cd, Hg, Pb and Sb, respectively. In particular, the extracted concentration of As, Cd, Hg and Sb are in excess of the tolerable levels. Positive correlation with organic matter and clay content but not with pH has been observed for most of elements analyzed in this study. Enrichment factor (EF) analysis and cluster analysis (CA) highlighted the lithogenic origin of heavy metals. It also revealed the need for detailed geochemical surveys in the future in order to decrease the uncertainty of discrimination between lithogenic and anthropogenic origin of metals of interest.

Heavy metals in soils: Distribution, relationship with soil characteristics and radionuclides and multivariate assessment of contamination sources

The study is dealing with the distribution and the origin of heavy metals (Cd, Cr, Cu, Mn, Ni, Pb and Zn) in soils from a priori non-polluted areas. Positive correlations with organic matter and clay content but not with pH have been observed for most of elements analyzed in this study. Correlations of some metals (Cr, Pb and Zn) and radionuclides ( 238U and 137Cs) observed for analyzed soils could be explained by their common affinity for clay minerals. Enrichment factor (EF) analysis and cluster analysis (CA) highlighted the lithogenic origin of Cr, Cu, Mn, Ni, Pb and Zn and pointed out the primary input of Cd from anthropogenic sources. It also revealed the need for detailed geochemical surveys in the future in order to decrease the uncertainty of discrimination between lithogenic and anthropogenic origin of metals of interest.

Carbon dioxide and radon gas hazard in the Alban Hills area (central Italy)

The sudden and catastrophic, or slow and continuous, release at surface of naturally occurring toxic gases like CO 2, H 2S and Rn poses a serious health risk to people living in geologically active regions. In general this problem receives little attention from local governments, although public concern is raised periodically when anomalous toxic-gas concentrations suddenly kill humans or livestock. For example, elevated CO 2 concentrations have been linked to the death of at least 10 people in the central Italian region of Lazio over the last 20 years, while it was the CO 2 asphyxiation of 30 cows in a heavily populated area near Rome in 1999 which prompted the present soil-gas study into the distribution of the local health risk. A detailed geochemical survey was carried out in an area of about 4 km 2 in the Ciampino and Marino districts, whereby a total of 274 soil-gas samples were collected and analysed for more than 10 major and trace gas species. Data were then processed using both statistical and geostatistical methods, and the resulting maps were examined in order to highlight areas of elevated risk. General trends of elevated CO 2 and Rn concentrations imply the presence of preferential pathways (i.e. faults and fractures) along which deep gases are able to migrate towards the surface. The CO 2 and Rn anomalous trends often correspond to and are usually elongated parallel to the Apennine mountain range, the controlling structural feature in central Italy. Because of this fundamental anisotropy in the factors controlling the soil-gas distribution, it was found that a geostatistical approach using variogram analysis allowed for a better interpretation of the data. With regard to the health risk to local inhabitants, it was found that although some high risk areas had been zoned as parkland, others had been heavily developed for residential purposes. For example, many new houses were found to have been built on ground which has soil-gas CO 2 concentrations of more than 70% and radon values of more than 250 kBq m −3. It is recommended that land-use planners incorporate soil-gas and/or gas flux measurements in environmental assessments in areas of possible risk (i.e. volcanic or structurally active areas).

Spatial variability of metals in the inter-tidal sediments of the Medway Estuary, Kent, UK

Concentrations of major and trace metals were determined in eight sediment cores collected from the inter-tidal zone of the Medway Estuary, Kent, UK. Metal associations and potential sources have been investigated using principal component analysis. These data provide the first detailed geochemical survey of recent sediments in the Medway Estuary. Metal concentrations in surface sediments lie in the mid to lower range for UK estuarine sediments indicating that the Medway receives low but appreciable contaminant inputs. Vertical metal distributions reveal variable redox zonation across the estuary and historically elevated anthropogenic inputs. Peak concentrations of Cu, Pb and Zn can be traced laterally across the estuary and their positions indicate periods of past erosion and/or non-deposition. However, low rates of sediment accumulation do not allow these sub surface maxima to be used as accurate geochemical marker horizons. The salt marshes and inter-tidal mud flats in the Medway Estuary are experiencing erosion, however the erosion of historically contaminated sediments is unlikely to re-release significant amounts of heavy metals to the estuarine system.

About this title

This volume describes the use of till geochemical and indicator mineral methods for mineral exploration in glaciated terrain of Canada. The principles and examples described in this volume wil have direct applications for exploration companies and prospectors exploring for diamonds, precious and base metals and uranium in glaciated parts of North America, northern Europe and Asia and mountainous regions of South America. The first two papers in this volume provide an introduction to glaciated terrain and the two styles of glaciation that have affected the world, continental glaciers in broad flat lying Shield areas and alpine glaciers in mountainous terrain. Sampling techniques are described next, followed by an introduction to the use of heavy minerals. Heavy mineral methodss have become an important exploration tool in glaciated terrain for gold and base metals and, in the last ten years, for diamonds. Lake sediments and biogeochemical methods are also included in this volume as a complement to geochemical and indicator mineral methods in glaciated terrain. A chapter on GIS has been included because data interpretation and display are important and essential parts of any regional or detailed geochemical survey. The remainder of the volume is case studies for the three main glaciated terrain tyes in Canada: Shield, Appalachia and Cordillera

Adjusting stream-sediment geochemical maps in the Austrian Bohemian Massif by analysis of variance

The Austrian portion of the Bohemian Massif is a Precambrian terrane composed mostly of highly metamorphosed rocks intruded by a series of granitoids that are petrographically similar. Rocks are exposed poorly and the subtle variations in rock type are difficult to map in the field. A detailed geochemical survey of stream sediments in this region has been conducted and included as part of the Geochemischer Atlas der Republik Osterreich,and the variations in stream sediment composition may help refine the geological interpretation. In an earlier study, multivariate analysis of variance (MANOVA) was applied to the stream-sediment data in order to minimize unwanted sampling variation and emphasize relationships between stream sediments and rock types in sample catchment areas. The estimated coefficients were used successfully to correct for the sampling effects throughout most of the region, but also introduced an overcorrection in some areas that seems to result from consistent but subtle differences in composition of specific rock types. By expanding the model to include an additional factor reflecting the presence of a major tectonic unit, the Rohrbach block, the overcorrection is removed. This iterative process simultaneously refines both the geochemical map by removing extraneous variation and the geological map by suggesting a more detailed classification of rock types.

Detailed geochemical survey in the Peloritani Arc (northeastern Sicily, Italy): Evidence of gold anomalies

A detailed geochemical survey has identified diffuse Au anomalies in the Peloritani Mountains (northeastern Sicily). The survey, which was carried out in two sectors of the Peloritani chain and covered an area of about 435 km2, involved the sampling of 1198 stream sediments. The area is well known for Pb, Zn, Cu and Sb mineralization, which has been mined on a small scale. Univariate and multivariate (R-mode factor and cluster analyses) statistical techniques have been used to interpret and evaluate the geochemical data. These have been complemented by mineralogical studies of 1099 samples of alluvial pan and heavy liquid concentrates. The statistical analysis has identified areas of anomalous Au, as well as As, Hg, Sb, Zn and Pb concentrations. The Au anomalies are distributed in a belt along the thrust contact of two metamorphic Hercynian units: the Aspromonte Unit (mostly high-grade metamorphic rocks) and the Mandanici Unit (mostly low-grade metamorphic rocks). In addition to Au anomalies ( >100 ppb and up to 1500 ppb) in stream sediments, Au flakes (between 100 and 400 μm in size) have been found along the “auriferous belt”.

Reconnaissance and detailed geochemical surveys for gold in eastern Nova Scotia using plants, lake sediment, soil and till

Reconnaissance-level geochemical surveys of similar sample density and areal extent were conducted using lake sediment and twigs of balsam fir ( Abies balsamea). Both sample media successfully delineate Au districts in eastern Nova Scotia. A moderately good spatial relationship between the data sets for Au and As suggests that either sample medium may be used to identify gold-bearing zones. Detailed sampling near gold mineralization permitted comparison of distribution patterns of Au, As and Sb in outer bark of red spruce ( Picea rubens), and several size fractions of till and B-horizon soil. Gold and As are enriched in all sample media (and in most size fractions) over a zone of glacial dispersal from the concealed mineralization. Appreciable enrichment of Sb occurs only in the spruce bark. Results show that either soil or spruce bark could be used to establish targets for more labour-intensive close-spaced sampling of heavy mineral concentrates in till.

Geochemical exploration for mineralized breccia pipes in northern Arizona, U.S.A.

Thousands of solution-collapse breccia pipe crop out in the canyons and on the plateaus of northern Arizona. Over 80 of these are known to contain U or Cu mineralized rock. The high-grade U ore associated with potentially economic concentrations of Ag, Pb, Zn, Cu, Co and Ni in some of these pipes has continued to stimulate mining and exploration activity in northern Arizona, despite periods of depressed U prices. Large expanses of northern Arizona are comprised of undissected high plateaus; recognition of pipes in these areas is particularly important because mining access to the plateaus is far better than to the canyons. The small size of the pipes, generally less than 600 ft (200 m) in diameter, and limited rock outcrop on the plateaus, compounds the recognition problem. Although the breccia pipes, which bottom in the Mississippian Redwall Limestone, are occasionally exposed on the plateaus as circular features, so are unmineralized near-surface collapse features that bottom in the Permian Kaibab and Toroweap Formations. The distinction between these two classes of circular features is critical during exploration for this unique type of U deposit. Various geochemical and geophysical exploration methods have been tested over these classes of collapse features. Because of the small size of the deposits, and the low-level geochemical signatures in the overlying rock that are rarely dispersed for distances in excess of several hundred feet, most reconnaissance geochemical surveys, such as hydrogeochemistry or stream sediment, will not delineete mineralized pipes. Several types of detailed geochemical surveys made over collapse features, located through examination of aerial photographs and later field mapping, have been successful at delineating collapse features from the surrounding host rock: (1) Rock geochemistry commonly shows low level Ag, As, Ba, Co, Cu, Ni, Pb, Se and Zn anomalies over mineralized breccia pipes; (2) Soil surveys appear to have the greatest potential for distinguishing mineralized breccia pipes from the surrounding terrane. Although the soil anomalies are only twice the background concentrations for most anomalous elements, traverses made over collapse features show consistent enrichment inside of the feature as compared to outside; (3) B. Cereus surveys over a known mineralized pipe show significantly more anomalous samples collected from within the ring fracture than from outside of the breccia pipe; (4) Helium soil-gas surveys were made over 7 collapse features with discouraging results from 5 of the 7 features. Geophysical surveys indicate that scaler audio-magnetotelluric (AMT) and E-field telluric profile data show diagnostic conductivity differences over mineralized pipes as compared to the surrounding terrane. These surveys, coupled with the geochemical surveys conducted as detailed studies over features mapped by field and aerial photograph examination, can be a significant asset in the selection of potential breccia pipes for drilling.

Computerized interpretation of a detailed geochemical survey on the Salvy prospect (southwest France)

Computerized interpretation of a detailed geochemical survey on the Salvy prospect (southwest France)