Prediction of true classes of surficial and deep earth materials using multivariate spatial data is a common challenge for geoscience modelers. Most geological processes leave a footprint that can be explored by geochemical data analysis. These footprints are normally complex statistical and spatial patterns buried deep in the high-dimensional compositional space. This paper proposes a spatial predictive model for classification of surficial and deep earth materials derived from the geochemical composition of surface regolith. The model is based on a combination of geostatistical simulation and machine learning approaches. A random forest predictive model is trained, and features are ranked based on their contribution to the predictive model. To generate potential and uncertainty maps, compositional data are simulated at unsampled locations via a chain of transformations (isometric log-ratio transformation followed by the flow anamorphosis) and geostatistical simulation. The simulated results are subsequently back-transformed to the original compositional space. The trained predictive model is used to estimate the probability of classes for simulated compositions. The proposed approach is illustrated through two case studies. In the first case study, the major crustal blocks of the Australian continent are predicted from the surface regolith geochemistry of the National Geochemical Survey of Australia project. The aim of the second case study is to discover the superficial deposits (peat) from the regional-scale soil geochemical data of the Tellus Project. The accuracy of the results in these two case studies confirms the usefulness of the proposed method for geological class prediction and geological process discovery.
Understanding the character of Australia's extensive regolith cover is crucial to the continuing success of mineral exploration. We hypothesise that the regolith contains geochemical fingerprints of processes related to the development and preservation of mineral systems at a range of scales. We test this hypothesis by analysing the composition of surface sediments within greenfield regional-scale (southern Thomson Orogen) and continental-scale (Australia) study areas. In the southern Thomson Orogen area, the first principal component (PC1) derived in our study [Ca, Sr, Cu, Mg, Au and Mo at one end; rare earth elements (REEs) and Th at the other] is very similar to the empirical vector used by a local company (enrichment in Sr, Ca and Au concomitant with depletion in REEs) to successfully site exploration drill holes for Cu–Au mineralisation. Mapping of the spatial distribution of PC1 in the region reveals several areas of elevated values and possible mineralisation potential. One of the strongest targets in the PC1 map is located between Brewarrina and Bourke in northern New South Wales. Here, exploration drilling has intersected porphyry Cu–Au mineralisation with up to 1 wt% Cu, 0.1 g/t Au, and 717 ppm Zn. The analysis of a comparable geochemical dataset at the continental scale yields a compositionally similar PC1 (Ca, Sr, Mg, Cu, Au and Mo at one end; REEs and Th at the other) to that of the regional study. Mapping PC1 at the continental scale shows patterns that (1) are spatially compatible with the regional study and (2) reveal several geological regions of elevated values, possibly suggesting an enhanced potential for porphyry Cu–Au mineralisation. These include well-endowed mineral provinces such as the Curnamona and Capricorn regions, but also some greenfield regions such as the Albany-Fraser/western Eucla, western Murray and Eromanga geological regions. We conclude that the geochemical composition of Australia's regolith may hold critical information pertaining to mineralisation within/beneath it. 相似文献
Mathematical Geosciences - Mineral deposits are metal enrichment anomalies, occurring as local manifestations of the interplay between various geological processes that operate at a wide range of... 相似文献
This study reviews the available information for over 1200 Australian salt lakes including in areas that have little or unreliable data. Publicly available groundwater hydrogeochemical datasets for the Australian arid zone are particularly sparse, inconsistent and of variable quality. Many datasets in the vicinity of salt lakes only report salinity or total dissolved solids, with no data for constituent cations and anions, and no appreciation of the hydrological and geomorphic evolution of the lakes. To overcome these limitations and to provide a broad-scale context, we developed mineral systems models to assess the potential of Australian salt lakes for potash, lithium and boron deposits. These models show that an important control on the potential of salt lake systems to form economic deposits of potash, lithium or boron is hydrogeological connectivity between leachable source rocks and the lakes. The assessment of the mineral potential was carried out in two stages. The first stage selection was based on the presence of favourable source rocks in the salt lakes’ catchments. The mean values of concentration in each catchment were derived from whole rock, sediment and groundwater geochemical datasets by averaging the values in samples (separately for each of the three datasets) located in the catchment and assigning this value to the catchment's salt lakes. The second stage selection was carried out by analysing available chemical data of groundwater in proximity to the salt lake systems delineated in the first stage. As a result, six regions were identified as having the highest potential, for potash in particular, but also for lithium and/or boron deposits. These are: the Lake Frome/Central Gawler Region of South Australia; two regions in the Northern Territory: the central western region extending into Western Australia, and the Lake Woods region; and, in Western Australia, the Lake Disappointment region, the north east Yilgarn and south east Yilgarn regions. 相似文献
Groundwater chemical data from Birkenes, southern Norway, collected during the period October 1980 to November 1993, reveal intensifying acidification in the 1990s, as evidenced by decreases in pH, acid-neutralising capacity and alkalinity, and increases in hardness/alkalinity ratio, ‘acidification’, nitrate, non-marine sulphate (SO4*), non-marine hardness (Ca* + Mg*) and dissolved aluminium. The whole monitoring period is characterised by slopes of four or more on a plot of (Ca* + Mg*) vs. alkalinity.
Owing to its proximity to the sea, the Birkenes catchment receives seasalt-influenced precipitation, which results in episodic, natural acidification of the groundwater via cation exchange of marine Na+ with soil-bound H+ and/or Al3+. However, it is uncertain whether all of the recent groundwater acidification can be attributed to intensifying seasalt deposition alone: the steep slopes on the (Ca* + Mg*) vs. alkalinity plot and the increase in groundwater SO4* suggest that strong acids, of possible anthropogenic origin, may be involved. Additionally, seasalt deposition appears not to have increased during the 1990s: Cl− content in precipitation has not increased significantly and river water pH has not decreased significantly over the period 1990–1993. The suggestion is made that the observed intensification in groundwater acidification at Birkenes partly results from the exhaustion or weakening of an acid buffering system caused by soil acidification, under persisting, even if abating, anthropogenic acid loading. 相似文献
We collected 38 groundwater and two surface-water samples in the semi-arid Lake Woods region of the Northern Territory to better understand the hydrogeochemistry of this system, which straddles the Wiso, Tennant Creek and Georgina geological regions. Lake Woods is presently a losing waterbody feeding the underlying groundwater system. The main aquifers comprise mainly carbonate (limestone and dolostone), siliciclastic (sandstone and siltstone) and evaporitic units. The water composition was determined in terms of bulk properties (pH, electrical conductivity, temperature, dissolved oxygen, redox potential), 40 major, minor and trace elements, and six isotopes (δ18Owater, δ2Hwater, δ13CDIC, δ34SSO42–, δ18OSO42–, 87Sr/86Sr). The groundwater is recharged through infiltration in the catchment from monsoonal rainfall (annual average rainfall ～600?mm) and runoff. It evolves geochemically mainly through evapotranspiration and water–mineral interaction (dissolution of carbonates, silicates and to a lesser extent sulfates). The two surface waters (one from the main creek feeding the lake, the other from the lake itself) are extraordinarily enriched in 18O and 2H isotopes (δ18O of +10.9 and +16.4‰ VSMOW, and δ2H of +41 and +93‰ VSMOW, respectively), which is interpreted to reflect evaporation during the dry season (annual average evaporation ～3000?mm) under low humidity conditions (annual average relative humidity ～40%). This interpretation is supported by modelling results. The potassium (K) relative enrichment (K/Cl– mass ratio over 50 times that of sea water) is similar to that observed in salt-lake systems worldwide that are prospective for potash resources. Potassium enrichment is believed to derive partly from dust during atmospheric transport/deposition, but mostly from weathering of K-silicates in the aquifer materials (and possibly underlying formations). Further studies of Australian salt-lake systems are required to reach evidence-based conclusions on their mineral potential for potash, lithium, boron and other low-temperature mineral system commodities such as uranium. 相似文献
The 42 element, 1190 sample Mobile Metal Ion subset of the National Geochemical Survey of Australia database was used to develop and illustrate the concept of Degree of Geochemical Similarity of soil samples. Element concentrations were unified to parts per million units and log(10)-transformed. The degree of similarity of pairs of samples of known provenance in the Yilgarn Craton was obtained using least-squares linear regression analysis and demonstrated that the method successfully assessed the degree of similarity of soils related to granitoid and greenstone lithologies. Exploratory Data Analysis symbol maps of all remaining samples in the database against various reference samples were used to obtain correlation maps not only for granitoid- and greenstone-related soil types but also to distinguish between, for example, samples derived from marine vs regolith carbonate. Likewise, the distribution of soil samples having a geochemical fingerprint similar to mineralised provinces (e.g. Mount Isa) can be mapped, and this can be used as a first-order prospection tool. 相似文献
This paper shows how constraints can be placed on the prediction of quartz equilibration distance in subsurface water flows. This is achieved here by coupling kinetic equations for the simple (SiO2(quartz)-H2O(water)) system to various groundwater flow parameters (compaction flow, aquifer, convection flow, and hydrothermal system). This approach determines: (1) the order of magnitude of the downstream distance necessary for equilibrium to be attained, when a flowing solution is initially out of equilibrium; and (2) the minimum flow velocity required to sustain a sufficient quartz undersaturation or oversaturation over a given distance. Geological conditions under which specific water-rock interactions take place can be constrained with those calculations. Water flow in most subsurface environments, as idealized here, tends to equilibrate with the quartz-rich hosting medium on a very short distance (≤ 1 m). Major exceptions are: (1) the topmost part of a compacting pile, (2) shallow and fast-flowing aquifers, and (3) most hydrothermal systems. 相似文献
Top and bottom samples of overbank sediments were collected at 43 sites within a 12 000 km2 area around the nickel smelter in Nikel and the ore roasting plant at Zapoljarnij, in northwestern Russia. In addition, three
detailed overbank profiles were sampled in 10-cm sections from three catchments representing different levels of pollution.
All samples were analysed for more than 30 elements by ICP-AES following aqua regia extraction. Results obtained show that
overbank sediments represent natural (geogenic) background levels rather well. Although the major pollutants (Co, Cu, Ni and
S) are strongly enriched at some places close to industry, overbank sediment is not especially well suited for mapping the
extent of airborne contamination in the area. Co, Cu, Ni and S are mobile within the profile collected from the most polluted
catchment.
Received: 23 July 1996 · Accepted 18 October 1996 相似文献
