Mineral Exploration Applications Research Articles

Handbook of Geochemistry: Techniques and Applications in Mineral Exploration

R. Dhana Raju. Pp. 520. 2009. Geological Society of India: Bangalore. ISBN 978-81-85867-93-9. US $70 (soft cover). The Handbook of Geochemistry is a compilation divided into one series of chapters on analytical techniques, and a second series of chapters on exploration geochemistry and isotope geochemistry. The Introduction to the book notes that the many different disciplines of geology critical to exploration are presented in numerous basic scientific papers scattered throughout the literature and there is a need for a comprehensive summary of such work that is presented to explorationists in a more applied manner. Raju does go on to admit that there are indeed some journals and texts that are more applied and useful to explorationists, but he claims they are not easily available to many academics in India and other developing countries because of high cost. Therefore, he hopes this book can represent a low-cost alternative to aid academics, exploration geologists, metallurgists, and managers in …

A flowline map of glaciated Canada based on remote sensing dataThis paper is accompanied by a large foldout map entitled A flowline map of glaciated Canada based on remote sensing data (see pocket on back cover).

The map A flowline map of glaciated Canada based on remote sensing data presents flowlines for the former Laurentide and Cordilleran ice sheets based on flow indicators derived from aggregated, flow-parallel landforms — drumlins and crag and tails, fluting, sinuous ridges and furrows, and rises. An extensive review introduces the concepts and evolution of flowline mapping at continental-ice-sheet and regional scales, emphasizing the use of new remote sensing data. Coherent, glaciologically plausible sets of flowlines mapped as flow tracts reflect large-scale flow structure in the paleo-ice sheets and demarcate fields of flow-parallel bedforms. In addition to flow reconstruction, mapped distributions of fields of glacial terrain types — hummocky terrain, Rogen terrain, and bedrock-dominant terrain — increase our power to interpret flowlines and, in turn, give evidence on the genesis of these terrains. End moraines and eskers also aid map interpretation. Landsat 7 Enhanced Thematic Mapper+ (ETM+) satellite images and Shuttle Radar Topography Mission (SRTM) hill shades provide the basic information for this flowline mapping in a Geographical Information System (ArcMap). Information on the Flowline Map allows us to develop conceptual models of ice sheets and to appreciate regional constraints on applications in mineral exploration, in aggregate and groundwater discovery and assessment, in soil and landform genesis, and in glaciology, paleoclimatology, and paleoceanography.

Usage of ERS SAR data over the Singhbhum Shear Zone, India for structural mapping and tectonic studies

The extraction of lineaments and anomalous patterns in the Singhbhum Shear Zone, Jharkhand, India, has multifaceted applications for mineral exploration as well as for geological interpretation of neotectonic movements. ERS-1 SAR data are very useful for such applications because of their structural information content. A comparative study has been attempted with ERS, Landsat and IRS images for the interpretation of various geological structures over the Singhbhum Shear Zone. The Rose diagram generated from this study has shown major trends that matched well with the geological map of the area and the associated tectonic boundary as well as with the results obtained from ground based studies.

Lithogeochemistry, C-O isotopes and Stratabound Alteration Halos to Stratiform Copper Mineralisation, Zambian Copperbelt

Summary A major lithogeochemical study of the basin sediments surrounding the stratiform copper deposits of the Zambian Copper Belt has revealed extensive stratabound zones of both potassic and sodic alteration. The syn-ore potassic alteration is represented by enrichment of biotite and K-feldspar in the enclosing sediments, with whole rock K 2 O values varying from 3.5 to 10 wt%. The sodic alteration (albite-calcite), post-dates the copper mineralisation, and occurs in the Upper Roan siltstone-carbonate sequence overlying the potassic alteration zone. Na 2 O values vary from 1.5 to 6.3 wt%, corresponding to a maximum of 60 wt% albite in the altered rock. A comprehensive study of carbon and oxygen isotopes of various carbonate types throughout the sediments of the Zambian Copper Belt has shown a systematic relationship to alteration and copper mineralisation that has significant application in mineral exploration. Mineralised and potassically altered zones show strong coupled depletion in both carbon and oxygen isotopes, with δ 13 C = -6 to ‐26 per mil and δ 18 O = 6 to 20 per mil. The strongly negative δ 13 C values of carbonate in the ore shale and potassic footwall clastics indicates the significant role of oxidation of organic carbon in the mineralising process. The fact that the relatively clean altered and mineralised footwall clastics also show this negative carbon isotope shift suggests that organic reaction products migrated out of the shale into the permeable footwall clastics prior to mixing with the ore fluid, leading to redox reactions causing coupled oxidation of organic matter and reduction of sulfate to H 2 S resulting in copper sulfide precipitation.

Development of a tri-directional helicopter gradiometer for mineral exploration applications

Development of a tri-directional helicopter gradiometer for mineral exploration applications

Scale Model Investigations of the Applied Potential Method for Crosshole Delineation of a Conductor

The Applied Potential method finds important application in mineral exploration. To better understand the detection and delineation capabilities of the technique, especially where (conductive) mineralisation is discontinuous, we have carried out a series of laboratory experiments using a 3D tank model system. Crosshole electric measurements were made with a bipole-bipole array, with one current electrode located in each simulated borehole. Both scanning (both bipoles moved together) and profiling measurements (using one fixed bipole and one mobile bipole) were conducted rather than full tomographic imaging. Five different classes of cylindrical model were studied, which were distinguished on the basis of (1) cylinder orientation relative to the plane of the boreholes, (2) whether the target was continuous, terminating, or broken between the points of measurement, and (3) whether the conductor was intersected by one or both boreholes. Each class of model produces a characteristic albeit complicated response, which can be used to identify the conductor and roughly locate its upper and lower boundaries. Data were collected for different bipole separations. Pronounced anomalies are produced for the scanning arrangement for models involving conductor intersection, although it is difficult to always distinguish the models and interpret the data. The character is very dependent on the electrode configuration relative to the target. Electric profiling produces a subtler and less diagnostic pattern, which is hard to discriminate from a background variation. The examples presented provide useful guidance when designing mise-á-la-masse or Applied Potential surveys. Moreover, they indicate that full tomographic imaging is required for all but the simplest cases.

GETMAG – a new magnetic tensor gradiometer for exploration

CSIRO and Australian exploration companies have developed a new instrument for mineral exploration.The GETMAG (Glass Earth Tensor Magnetic Airborne Gradiometer) instrument measures the magnetic gradient tensor and the components of the magnetic field. The sensors are high temperature superconducting (HTS) quantum interference devices (SQUIDs) operating at liquid nitrogen temperature. A superconducting transformer coupled to a SQUID magnetometer is rotated to detect all gradients perpendicular to the rotation axis. Three SQUID-loop assemblies are required to measure the full tensor.Field trials demonstrate that the inversion of a few tensor measurements yields as much information as a high-resolution total magnetic intensity (TMI) survey. Direction to individual sources and their magnetic moments (reduced according to distance) can be determined directly from the tensor. GETMAG has applications in mineral exploration, environmental studies, ordnance detection, ship degaussing, submarine tracking and monitoring of marine currents.The project was funded by CSIRO, BHP, De Beers, MM, Newmont and WMC.

An appreciation of Daniel Robert Boyle, and an introduction to the special issue of Geochemistry: Exploration, Environment, Analysis in his honour

Daniel Robert Boyle,our friend and colleague, died on 29 June 2000, in Ottawa, Canada, at the age of 52 after a courageous battle with cancer. Dan was a leader at the Geological Survey of Canada (GSC) in the application of lithogeochemistry, and groundwater geochemistry for the study of mineral deposit genesis, mineral exploration, environmental and health issues. He was the son of the (recently deceased: 5 August 2003) internationally renowned and respected geochemist Bob(Robert W.) Boyle, who was also employed at the GSC (Garrett 2004). Growing up in the 1950s and 1960s, Dan spent many happy summers travelling with his family to places across Canada, notably New Brunswick and Nova Scotia, where his father's fieldwork took him. These experiences instilled in Dan and his sister Heather a love for the sciences and the outdoors that shaped both their future careers: Dan following in his father's footsteps as a geochemist, while Heather, the family radical, became a biochemist (Carleton University, Ottawa, Canada and Victoria University, Wellington, New Zealand). Dan completed a BSc honours degree at Queen's University at Kingston, Canada, with a thesis entitled “Geochemical environmental study over a Cu–Mo porphyry deposit, British Columbia”. He continued his education at the Imperial College of Science and Technology, University of London, London, UK. He graduated with a PhD in 1976, and his thesis was entitled “The geochemistry of fluorine and its application in mineral exploration“. During his studies in the UK, he completed several mineral exploration consulting contracts in Spain, France, Ireland, Turkey, and Great Britain. During the latter part of his PhD studies, he became a member of the Mineral Industry Research Organization review board of Great Britain. While at Imperial College, Dan became an associate professor, and later (1975) head of the mineral exploration research section of the applied geochemistry …

Short Wavelength Infrared (SWIR) Spectral Analysis ofHydrothermal Alteration Zones Associated with Base Metal Sulfide Depositsat Rosebery and Western Tharsis, Tasmania, and Highway-Reward, Queensland

Spectral analysis of rock samples by short wavelength infrared (SWIR) analysis, using the portable infrared mineral analyzer (PIMA) spectrometer, is a relatively new field method with applications in mineral exploration. The technique allows rapid field-based identification of hydrothermal alteration minerals and delineation of alteration zones. Variations in mineral composition, crystallinity, and relative abundance may also be determined. Phyllosilicates, including white mica and chlorite, are particularly amenable to short wavelength infrared analysis. These are prominent alteration minerals in the felsic volcanic rocks in the Mount Read Volcanics, Tasmania, and the Mount Windsor subprovince, North Queensland. They have regional distributions as diagenetic and metamorphic products and exist locally in alteration zones associated with volcanic-hosted sulfide deposits. A geochemical and spectral investigation of white micas in the least altered rocks in the Mount Read Volcanics has shown considerable background compositional variations. The white micas range from phengite to moderately sodic muscovite and SWIR spectral measurements provide reliable estimates of their compositions. Chlorites also have a broad compositional range in these rocks. However, SWIR spectral analysis has proven to be unreliable in determining chlorite composition in samples where chlorite exists in low proportions relative to white mica or in mixed assemblages with epidote. White micas in footwall alteration zones of the Rosebery stratiform Zn + Pb deposit (Tasmania) are variably phengitic, similar to those in regional background volcanics. A unit of relatively unaltered volcaniclastic sandstone in the Rosebery hanging-wall sequence contains anomalous sodic muscovite in proximity to ore lenses. White micas associated with the disseminated to massive pyritic Cu + Au deposits at Western Tharsis (Tasmania) and Highway-Reward (North Queensland) range in composition from phengite to slightly sodic muscovite. In these symmetrically zoned alteration systems, white micas grade in composition from phengite, in peripheral zones, to slightly sodic muscovite, in proximal zones near ore. In all three cases, the white mica compositional variation is a vector to ore that is effectively measured by SWIR spectrometry, with particular application in prospect-scale exploration. Chlorite compositions at Rosebery are not strictly spatially related to ore but tend to be most magnesian in zones of high chlorite abundance. In the outer alteration zone at Western Tharsis, there is a faint proximal trend to iron-rich chlorites. However, it does not represent a well-defined vector to ore in either case. Attempts at quantitative estimation of the relative abundance of white mica and chlorite in mixed samples, by spectral analysis, have produced results that are imprecise in comparison to geochemically derived estimates. The data scatter relates to the low proportions of chlorite in the majority of the samples analyzed, resulting in weak chlorite absorptions. Better results may be obtainable, in specific alteration or lithostratigraphic domains, by use of customized spectral unmixing software. This investigation has shown that PIMA-based SWIR spectrometry is a potent field method of mapping compositional variations in white micas that represent empirical vectors to at least some types of volcanic-hosted sulfide deposits. It has also highlighted its effectiveness in field identification of megascopically difficult or indeterminate alteration minerals, such as pyrophyllite, zunyite, and topaz, which may have genetic implications and exploration significance.

Measurement of static shift in MT and CSAMT surveys

Controlled source audio-frequency magnetotelluric (CSAMT) surveys have found frequent application in mineral exploration, and there have also been a number of attempts to use magnetotelluric (MT) soundings in the same application. The advantages of CSAMT over conventional electromagnetic methods lies in its ability (through measurements of the electric field) to discriminate resistive as well as conductive zones, and in its depth-of-penetration capability.“Static shift” however can be a common problem in many MT and CSAMT soundings. It severely distorts any depth calculations and degrades the resolution of conductivity structure inferred from scalar CSAMT measurements. Static shift also significantly restricts the MT-method in its use for geological studies of the upper and lower crust; and its application to mineral, hydrocarbon, and geothermal resource exploration. Theoretical investigation using modelling has shown that measurements of an Inductive Source Telluric Field (ISTF) may closely predict and thus potentially remove the static shift at MT and CSAMT stations.Applications of the method in the field require the additional setup of a low-power transmitter near the survey line. The main survey electrodes, cables and receiver are then used to collect additional data for corrections. This process can be run in parallel with the MT or CSAMT data acquisition, and requires little additional survey time. Initial tests of the concept in field studies near Sydney and over a skarn prospect in the Parkes vicinity proved very encouraging. The ‘along-line variation’ indicative of static shift was reduced by the correction by a factor of about 5 in the Parkes case, and the ‘corrected’ CSAMT section appeared smooth and regular as opposed to having the vertical striping typical of static problems.

Application of bulk sand geochemistry in mineral exploration and Quaternary research: a methodological study of the Allier and Dore terrace sands, Limagne rift valley, France

The bulk geochemistry of unconsolidated sands from river terraces in two drainage basins of contrasting geology in the Limagne rift valley, France, was studied. Data processing and interpretation was done with multivariate statistics, notably factor analysis. In the Allier drainage basin, underlain by volcanic rocks and crystalline basement, the abundance of basaltic rock fragments causes significantly higher bulk concentrations of TiO 2, Al 2O 3, Fe 2O 3, MgO, CaO, P 2O 5, V, Cr, Ni, Zn, Sr, Zr and Nb. In the Dore basin, underlain only by crystalline basement, sands have a significantly higher SiO 2, K 2O, Rb and Pb content, originating from quartz, K-feldspars and micas. Comparison between different terrace levels shows the impact of weathering and changes in supplied sediment composition over time. Approximately 65% of the total variance in the basaltic element content in the Allier terrace sands can be explained by the combined effect of parent material and weathering. The effect of grain size on sediment composition is only significant for Al 2O 3, Na 2O and Rb content in the Allier sands, and for TiO 2, Fe 2O 3 and Nb content in the Dore sands. Approximately 60% of the total variability in these elements is grain-size related. These results show that the technique of studying the bulk geochemical composition of stream sediments has direct applications for mineral exploration and Quaternary research.

Application of Regional Geochemical Data to Uranium Exploration: ABSTRACT

Hydrogeochemical and stream-sediment reconnaissance data generated by the U.S. Department of Energy's National Uranium Resource Evaluation program can be used to identify geologic environments favorable for uranium or base metal deposits. Open-filed analytical data for 1 × 2° NTMS quadrangles are obtained on magnetic tape from Oak Ridge National Laboratory and transferred to disk for interactive computer use. Data may then be organized into subsets according to sample type, geologic, or physiographic units; smoothed using block or nearest-neighbor averaging techniques; and power transformed to normalize frequency distributions. Multivariate statistical techniques, including principal component, discriminant, and multiple regression analyses, aid in interpretation. A contrast filter may be used to identify areas that are significantly different from their local background. Machine-generated color or black and white maps are produced from raw elemental analyses, elemental ratios, and statistical parameters such as factor scores and multiple regression residuals. The data may be represented at any scale, using a variety of symbol or color schemes designed to cartographically enhance the appearance of anomalous areas. Results of the geochemical interpretation are used to select target areas several tens of square kilometers in size. Examples from the Colorado Plateau and other areas illustrate how the interpretive techniques are used. Both the data and data analysis techniques have wide application in mineral exploration. Because of the extensive suite of elements represented, the data can be End_Page 695------------------------------ beneficial to any organization involved in frontier exploration for uranium or base metals. End_of_Article - Last_Page 696------------

Application of discriminant analysis to evaluate compositional controls of stratiform massive sulfide deposits in Canada

Multiple discriminant analysis is used to identify systematic variations of Cu, Pb, Zn, Ag, and Au grade values in the Canadian massive sulfide deposits with the three geological parameters of age, environment, and composition of volcanic lithology. The deposits have been separated into three groups on each of the three parameter scales and discriminant functions that separated the three groups on the basis of metal grades were then obtained. The results of the analysis indicated that Pb and Cu are the most significant in indicating specific trends along the three geological parameter scales. Pb grade increases in younger deposits with an increase in the sedimentary character of their environments, or with a more felsic nature to their volcanic rocks. On the other hand, Cu grade increases in deposits that occur in volcanic environments and with a more mafic nature to the volcanic host rocks. The results could have useful applications in mineral exploration.

Remote-sensing applications for mineral exploration [book review

Remote-sensing applications for mineral exploration [book review