Biogeochemical Methods Research Articles

Application of orientation biogeochemical exploration method in the vicinity of Ildong Fe-Pb-Zn skarn deposits in Korea

Orientation biogeochemical exploration was applied in the vicinity of Ildong Fe-Pb-Zn skarn deposits in Korea. Sampling was conducted along four traverse lines and control areas. A total of 12 rock, 64 soil and 320 plant samples (including three species such as Daimyo oak leaves/branches (Quercus dentata), Ash tree leaves/branches (Fraxinus rhynchophylla Hance) and Japanese red pine leaves (Pinus densiflora Siebold & Zucc.)) were collected and analysed. The content of Cu, Pb, Zn, Mn, Cd, As and Mo in soil from target areas (n = 56) were 2.0–4.5 times higher than those from control areas (n = 8). However, there were no specific contrasts of element content in plant samples (each n = 56) except both for Pb in Q. dentata leaves (0.45–54.93 mg/kg Pb) and branches (0.73–25.89 mg/kg Pb) and Cd in P. densiflora leaves (0.06–4.08 mg/kg Cd). The biological absorption coefficient for each plant sample was low, except for Cd and Mo, which shows 0.214 and 0.149 respectively in P. densiflora. Also, element content in soils and P. densiflora leaves is positively correlated and these geochemical variations of Cd and Mo show similar trends. Therefore, P. densiflora leaves showed the possibility of Cd and Mo indicator in these types of deposits.

New phytoplankton production as a tool to estimate the vertical component of water exchange between the Gulf of California and the Pacific

Water exchange between the Gulf of California and the Pacific has a significant vertical component. Surface (0–200 m) gulf water flows out into the Pacific and deep (200–600 m) water flows into the gulf. A biogeochemical method is proposed to estimate this vertical component of water exchange assuming steady state for the concentration of nutrients in the gulf and using the net average annual input of nitrate needed to support new phytoplankton production in the whole Gulf of California (PNEW). An annual average PNEW of (2586.7 ± 131.7) × 109 mol C yr–1 was deduced from the literature for the whole gulf and for non-El Niño years. Using the Redfield N:C ratio (16:122), the nitrate needed to support PNEW was estimated as (339 ± 17)× 109 mol yr–1. Annual representative averages of NO3, for the mouth of the gulf and for the depth intervals 0–200 m and 200–600 m, were used to calculate the annual average vertical component of water exchange between the gulf and the Pacific to balance the nitrate needed to support PNEW with the net input of nitrate from the Pacific, and the result was (0.67 ± 0.10) Sv in and out of the gulf. This relatively low value, possibly only ~7% of the whole water exchange, indicates that when considering a particular depth most of the time the inflow from the Pacific is equal or very similar to the outflow. Thus, most of the exchange between the gulf and the Pacific consists of the horizontal component.

Biomolecular and micromorphological analysis of suspected faecal deposits at Neolithic Çatalhöyük, Turkey

Suspected coprolites from midden, burial and room fill contexts at Çatalhöyük were analysed by GC/MS and thin section micromorphology. Assessment of sterol biomarkers enabled a distinction between faecal and non-faecal sources for the deposits to be made, with bile acid biomarkers indicating that many of the faecal deposits are human coprolites. The relative lack of ruminant faeces could be due to this material being used as a fuel source. Deposits in burials were observed to contain soil and plant derived sterols rather than their faecal counterparts. Further analysis in thin section enabled identification of associated materials and contents. Diagnostic inclusions such as bone and plant fragments were only present in some of the human coprolites, which were observed to have a very similar morphology to decayed plant remains. This study illustrates the difficulties in distinguishing coprolites in the field and under the microscope, and demonstrates the importance of integrating biogeochemical methods, particularly when such deposits are used as the basis for interpreting human health and diet, and use-of-space in settlements.

Potential relationships between atmospheric particulate matter transported by winter monsoons and red tides in the East China Sea

Combining numerical diagnosis from atmospheric science with biogeochemical methods, a model of the potential correlation of monsoons with red tide emergence in the East China Sea is constructed. The model is designed based on an in-depth investigation of the time-space relationship of aerosol and red tide events in the East China Sea from 2005 to 2006, and a continuous monitoring of atmospheric particulates at two stations. The study shows that every red tide event investigated has a close relationship with aerosols coming from the northwest (wind direction in winter) along with subsidence flow. The elemental abundance of total suspended particulate in Hangzhou and Tiantai is different from that of soil background levels, indicating atmospheric particulates there are brought in by winter winds. There is a significant correlation between the content of iron and phosphorous in atmospheric particulates, which mainly exist in binding materials between particulates. In addition, the confined absorption of iron and phosphorous by red tides is related to the intensity of sunlight. These results provide new information regarding the mechanism for the high frequency of red tides in the East China Sea. The results also provide a scientific basis for establishing new pathways for pre-warning and forecasting of red tide disasters.

Three-dimensional analysis of the structure and ecology of a novel, ultra-small archaeon

Fully understanding the biology of acid mine drainage (AMD) is central to our ability to control and manipulate its environmental impact. Although genomics and biogeochemical methods are relatively well established in the field, their combination with high-resolution imaging of intact members of microbial biofilm communities has not yet reached its full potential. Here, we used three-dimensional (3D) cryogenic electron tomography to determine the size and ultrastructure of intact ARMAN cells, a novel ultra-small archaeon, and sought evidence for their interactions with other members of its community. Within acid mine drainage biofilms, apparently free-living ARMAN cells from a deeply branched archaeal lineage have volumes of 0.009-0.04 microm(3) (mean approximately 0.03+/-0.01 microm(3)), only approximately 92 ribosomes, yet are frequent hosts for replicating viruses. Organization within the periplasm and partitioning of ribosomes to the inner surface of the cytoplasmic membrane may be factors in size minimization. Most cells contain enigmatic tubular structures of unknown function. The low ribosome copy number per unit volume, indicative of slow growth rates and targeting of cells by diverse viruses may account for the low abundance of ARMAN cells compared with other biofilm community members. Our results provide the first 3D analysis of structural features of these novel and enigmatic cells and their interactions with at least two types of viruses. Our findings also emphasize that new biological phenomena remain to be discovered among lower abundance organisms from novel uncultivated lineages.

Porewater biogeochemistry and soil metabolism in dwarf red mangrove habitats (Twin Cays, Belize)

Seasonal variability in biogeochemical signatures was used to elucidate the dominant pathways of soil microbial metabolism and elemental cycling in an oligotrophic mangrove system. Three interior dwarf mangrove habitats (Twin Cays, Belize) where surface soils were overlain by microbial mats were sampled during wet and dry periods of the year. Porewater equilibration meters and standard biogeochemical methods provided steady-state porewater profiles of pH, chloride, sulfate, sulfide, ammonium, nitrate/nitrite, phosphate, dissolved organic carbon, nitrogen, and phosphorus, reduced iron and manganese, dissolved inorganic carbon, methane and nitrous oxide. During the wet season, the salinity of overlying pond water and shallow porewaters decreased. Increased rainwater infiltration through soils combined with higher tidal heights appeared to result in increased organic carbon inventories and more reducing soil porewaters. During the dry season, evaporation increased both surface water and porewater salinities, while lower tidal heights resulted in less reduced soil porewaters. Rainfall strongly influenced inventories of dissolved organic carbon and nitrogen, possibly due to more rapid decay of mangrove litter during the wet season. During both times of year, high concentrations of reduced metabolites accumulated at depth, indicating substantial rates of organic matter mineralization coupled primarily to sulfate reduction. Nitrous oxide and methane concentrations were supersaturated indicating considerable rates of nitrification and/or incomplete denitrification and methanogenesis, respectively. More reducing soil conditions during the wet season promoted the production of reduced manganese. Contemporaneous activity of sulfate reduction and methanogenesis was likely fueled by the presence of noncompetitive substrates. The findings indicate that these interior dwarf areas are unique sites of nutrient and energy regeneration and may be critical to the overall persistence and productivity of mangrove-dominated islands in oligotrophic settings.

Geochemical characteristics of the modern state of salt lakes in Altai krai

A complex of analytical methods (atomic absorption spectroscopy AAS, synchrotron radiation X-ray fluorescence SR-XRF, and instrumental neutron activation analysis INAA) were used for analyses of 40 trace elements. In compliance with the conventional biogeochemical methods, enrichment factors EF were calculated for plankton relative to the average concentrations of elements in continental clay (shale) preliminarily normalized to Sc. In order to understand the concentration specifics of trace elements in living organisms inhabiting aquatic ecosystems of variable salt composition and geochemical characteristics, chemical speciation of elements was calculated for the brines of salt lakes by the WATEQ4F and Selektor-S computer programs. The enrichment of plankton in Hg in Lake Bol’shoe Yarovoe is caused not only by the chemistry of the mineralized brine (bittern), as follows from the Hg speciation in it, but also by anthropogenic contamination (Hg-bearing wastes from the Altaikhimprom chemical plants in the town of Yarovoe).

Biogeochemical characteristics of the Hetai goldfield, Guangdong Province, China

In the Hetai goldfield, Guangdong Province, China, samples including rocks, soils and leaves of four plants ( Pinus massoniana, Rhodomyrms tomenlosa, D. linearis var. dichotoma and Embelia laeta) collected from the gold mineralization zone and the background area were analyzed for Au, Ag, Cu, Pb, Zn, Hg, As and physiological parameters. The objective of this investigation is to study the geochemical and biogeochemical characteristics of studied plants, aiming at biogeochemical methods in Au exploration. The goldfield region shows geochemical and biogeochemical anomalies. Abundances of Au in rocks, soils, plants and the leaf pigments in the mineralized area are much higher than those in the surrounding region. The plants display unhealthy physiological and ecological characteristics in the Hetai goldfield area. The cell structures of the goldfield plants were anomalous and aberrant, and there were many nano-metal particles diffused in mitochondria and chloroplasts. Macro- and microscopic evidences of the vegetation in the goldfield areas are distinctly different from the background regions. The strongly anomalies in responses to Au are profound in further geochemical and botanic exploration studies.

Heavy metals in bark of Pinus massoniana (Lamb.) as an indicator of atmospheric deposition near a smeltery at Qujiang, China

Rapid urbanization and the expansion of industrial activities in the past several decades have led to large increases in emissions of pollutants in the Pearl River Delta of south China. Recent reports have suggested that industrial emission is a major factor contributing to the damages in current natural ecosystem in the Delta area. Tree barks have been used successfully to monitor the levels of atmospheric metal deposition in many areas, but rarely in China. This study aimed at determining whether atmospheric heavy metal deposition from a Pb-Zn smeltery at Qujiang, Guangdong province, could be accurately reflected both in the inner bark and the outer bark of Masson pine (Pinus massoniana L.). The impact of the emission from smeltery on the soils beneath the trees and the relationships of the concentrations between the soils and the barks were also analyzed. Barks around the bole of Pinus massoniana from a pine forest near a Pb-Zn smeltery at Qujiang and a reference forest at Dinghushan natural reserve were sampled with a stainless knife at an average height of 1.5 m above the ground. Mosses and lichens on the surface barks were cleaned prior to sampling. The samples were carefully divided into the inner bark (living part) and the outer bark (dead part) in the laboratory, and dried and ground, respectively. After being dry-ashed, the powder of the barks was dissolved in HNO3. The solutions were analyzed for iron (Fe), manganese (Mn), copper (Cu), zinc (Zn), chromium (Cr), nickel (Ni) and cobalt (Co) by inductively coupled plasmas emission spectrometry (ICP, PS-1000AT, USA) and Cadmium (Cd) and lead (Pb) by graphite furnace atomic absorption spectrometry (GFAAS, ZEENIT 60, Germany). Surface soils (0-10 cm) beneath the sample trees were also collected and analyzed for the selected metals. Concentrations of the selected metals in soils at Qujiang were far above their environmental background values in the area, except for Fe and Mn, whilst at Dinghushan, they were far below their background values, except for Cd and Co. Levels of the metals, in particular Pb and Zn, in the soils beneath the sample trees at Qujiang were higher than those at Dinghushan with statistical significance. The result suggested that the pine forest soils at Qujiang had a great input of heavy metals from wet and dry atmospheric deposition, with the Pb-Zn smeltery most probably being the source. Levels of Cu, Fe, Mn, Zn, Ni and Pb at Qujiang, both in the inner and the outer bark, were statistically higher than those at Dinghushan. Higher concentrations of Pb, Fe, Zn and Cu may come from the stem-flow of elements leached from the canopy, soil splash on the 1.5 m height and sorption of metals in the mosses and lichens growing on the bark, which were direct or indirect results from the atmospheric deposition. Levels of heavy metals in the outer barks were associated well with the metal concentrations in the soil, reflecting the close relationships between the metal atmospheric deposition and their accumulation in the outer bark of Masson pine. The significant (p<0.01) correlations of Fe-Cu, Fe-Cr, Fe-Pb, Fe-Ni, Pb-Ni, and Pb-Zn in the outer barks at Qujiang again suggested a common source for the metals. The correlation only occurred between Pb and Ni, Cd and Co in the outer barks at Dinghushan, which suggested that those metals must possibly have other uncommon sources. Atmospheric deposition of the selected metals was great at Qujiang, based on the levels in the bark of Pinus massoniana and on the concentrations in the soils beneath the trees compared with that at Dinghushan. Bark of Pinus massoniana, especially the outer bark, was an indicator of metal loading at least at the time of sampling. The results from this study and the techniques employed constituted a new contribution to the development of biogeochemical methods for environmental monitoring particularly in areas with high frequency of pollution in China. The method would be of value for follow up studies aimed at the assessment of industrial pollution in other areas similar with the Pearl River Delta.

Late Glacial and Holocene history of former Salziger See, Central Germany, and its climatic and environmental implications

An 8.40 m long sediment sequence from the Salziger See basin, Central Germany, was investigated by a multi-disciplinary approach including chronological, sedimentological, geo- and biogeochemical methods. Radiocarbon dating, conducted on ten samples of aquatic and terrestrial fossil remains, and the occurrence of the Laacher See Tephra (LST) reveal that the sediment sequence comprises the Late Glacial and Holocene lake history since ca. 13,800 cal. year BP. This onset of lacustrine sedimentation is almost 7,000 years earlier as assumed so far. The geo- and biogeochemical data indicate distinct variations throughout the Late Glacial, which can be correlated with cold and warm periods, such as the Oldest Dryas, the Bolling, the Allerod, and the Younger Dryas. During most of the Holocene, minor variations in the geo- and biogeochemical data and a high carbonate content due to the formation and precipitation of autochthonous carbonate in the lake indicate relatively stable lacustrine conditions. A slight change in the sedimentary conditions between 6,700 and 4,000 cal. year BP, with lower deposition of carbonate and fine material, can be traced back to enhanced subrosion in the basin. Increased deposition of coarser sediments and a high accumulation of heavy metals document intensive human activity in the region during the past ca. 1,000 years.

Biogeochemistry of an Iron-Rich Hypersaline Microbial Mat (Camargue, France)

In situ microsensor measurements were combined with biogeochemical methods to determine oxygen, sulfur, and carbon cycling in microbial mats growing in a solar saltern (Salin-de-Giraud, France). Sulfate reduction rates closely followed the daily temperature changes and were highest during the day at 25 degrees C and lowest during the night at 11 degrees C, most probably fueled by direct substrate interactions between cyanobacteria and sulfate-reducing bacteria. Sulfate reduction was the major mineralization process during the night and the contribution of aerobic respiration to nighttime DIC production decreased. This decrease of aerobic respiration led to an increasing contribution of sulfide (and iron) oxidation to nighttime O2 consumption. A peak of elemental sulfur in a layer of high sulfate reduction at low sulfide concentration underneath the oxic zone indicated anoxygenic photosynthesis and/or sulfide oxidation by iron, which strongly contributed to sulfide consumption. We found a significant internal carbon cycling in the mat, and sulfate reduction directly supplied DIC for photosynthesis. The mats were characterized by a high iron content of 56 micromol Fe cm(-3), and iron cycling strongly controlled the sulfur cycle in the mat. This included sulfide precipitation resulting in high FeS contents with depth, and reactions of iron oxides with sulfide, especially after sunset, leading to a pronounced gap between oxygen and sulfide gradients and an unusual persistence of a pH peak in the uppermost mat layer until midnight.

Diversity and vertical distribution of magnetotactic bacteria along chemical gradients in freshwater microcosms

The vertical distribution of magnetotactic bacteria along various physico-chemical gradients in freshwater microcosms was analyzed by a combined approach of viable cell counts, 16S rRNA gene analysis, microsensor profiling and biogeochemical methods. The occurrence of magnetotactic bacteria was restricted to a narrow sediment layer overlapping or closely below the maximum oxygen and nitrate penetration depth. Different species showed different preferences within vertical gradients, but the largest proportion (63–98%) of magnetotactic bacteria was detected within the suboxic zone. In one microcosm the community of magnetotactic bacteria was dominated by one species of a coccoid “ Alphaproteobacterium”, as detected by denaturing gradient gel electrophoresis in sediment horizons from 1 to 10 mm depth. Maximum numbers of magnetotactic bacteria were up to 1.5 × 10 7 cells/cm 3, which corresponded to 1% of the total cell number in the upper sediment layer. The occurrence of magnetotactic bacteria coincided with the availability of significant amounts (6–60 μM) of soluble Fe(II), and in one sample with hydrogen sulfide (up to 40 μM). Although various trends were clearly observed, a strict correlation between the distribution of magnetotactic bacteria and individual geochemical parameters was absent. This is discussed in terms of metabolic adaptation of various strains of magnetotactic bacteria to stratified sediments and diversity of the magnetotactic bacterial communities.

Biogeochemical Prospecting of Sulphide Minerals in Winder Valley, Balochistan, Pakistan

Abstract: The Mor Range is mountainous terrain in southern Balochistan dominantly occupied by exposures of rocks of the Ferozabad Group which is comprised of Lower‐Middle Jurassic carbonates and siliciclastics. This group contains syngenetic and epigenetic Zn–Pb–Ba mineralization classified as Stratiform Sediment‐Hosted (SSH) and Mississippi Valley Type (MVT) deposits. Three important flora of the Saharo–Sindian, phytogeographical region of Pakistan, namely Tamarix aphyl–la, Salvadora oleoides and Acacia arabica have been studied as a mineralization prospecting tool. Samples of these species were collected from Winder Valley adjoining the Mor Range to prospect for new areas of mineralization, besides the known sulphide deposits. This study revealed the Draber, Thorar, Raj, Mithi and Kanrach localities as new prospect. Quantitative estimation of biophile elements (Zn–Cu–Pb) from the three species was made. A number of new Zn, Cu and Pb anomalies were distinguished in the area. The variation in the constituents of these species from different localities possibly varies with nature and distance from bedrock, mobility, climate, average abundance in the plant ash and exclusion mechanism of the flora. Acacia arabica with deep penetrating roots shows the best results and could be used to delineate new horizons of mineralization. In these species Zn and Cu are relatively concentrated whereas Pb shows limited enrichment. Lead therefore is the element best suited for pinpointing the mineralization owing to its relatively less mobile character.Relationships among Zn–Cu–Pb have been established using scattergrams and triangular variation diagram, which also demonstrate their genetic affiliation. Statistical analyses, such as determination of mean, mode, median, standard deviation, and coefficient of correlation, were also made to improve the raw geochemical data. These biogeochemical methods appear to be suitable in arid climate of Balochistan, if proper attention is paid to species selection.

Biogeochemical exploration methods in the Canadian Shield and Cordillera

Abstract This review article focuses on field methods in biogeochemical exploration and is based largely on the author’s experience. Consideration is given to reasons for applying biogeochemical methods as alternatives or supplements to other surficial sampling media that can be used in the exploration for mineral deposits in glaciated terrain. Extensive root systems can absorb metals from the substrate and integrate the geochemical signature of large volumes of sediment, groundwater and sometimes bedrock, thereby providing a more representative reflection of the chemical environment than that obtained from some other media. Sampling methods and precautions that should be taken are outlined. Variables that govern plant chemistry include the heterogeneity of composition among plant species and plant tissues, and the modifying effects of the seasons and contamination from external sources. Studies indicate that biogeochemical methods can provide a more proximal indication of concealed mineralization than the distal indications typical of till geochemistry programmes. Consequently, comparisons of till and biogeochemical data can help to define vectors toward mineralized sources such that the two methods are complementary.

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

Biogeochemical exploration for massive sulphide deposits in areas of dense vegetation: an orientation survey around the Kanköy Deposit (Trabzon, northeastern Turkey)

The eastern Pontides region is a mountainous terrain favourable for massive sulphide deposits. Besides the known deposits, it is highly likely that there are others to be discovered. This paper, therefore, describes the results of a soil and biogeochemical sampling program to assess the suitability of biogeochemical methods for the exploration of hidden deposits in temperate terrains. Soil sampling in the Pontides is shown to be a reliable follow-up method. It produced a significant geochemical response characterised by extensive Cu and Zn but localised Pb anomalies. Lead therefore is the element which can be used to pinpoint the mineralisation due to its relatively less mobile character. Hydromorphic dispersion enhanced the anomalies indicating that base of slope samples would produce reliable results. Of the plant species sampled, Corylus avellana (hazelnut tree) with deep penetrating roots shows comparable results to soil sampling and could be used to delineate the mineralisation. Rhododendron luteum may also be of help. In both species Pb shows limited dispersion and accumulates in the plants near the mineralised site whereas Cu and Zn tend to move away downslope. This shows that biogeochemical sampling could, with proper attention to species selection, be successfully used as an alternative method in the search of massive sulphide deposits in mountainous terrains with a high rainfall such as the eastern Pontides.

Biogeochemical exploration for gold in tropical rain forest regions of Papua New Guinea

Biogeochemical methods have been widely used for mineral exploration, particularly in boreal forests and semi-arid regions, but there have been fewer applications in tropical areas. This paper describes a biogeochemical method of exploration for Au in equatorial regions. After investigation of several plant species, Astronidium palauense, a small- to moderate-size tree, was found to have many suitable attributes. (1) It is widely distributed in the southwest Pacific, although its occurrence may be limited at elevations greater than 1000 m. (2) The tree is easy to identify and is sufficiently common (e.g., one tree per 100 m 2 on Simberi and Lihir Islands, Papua New Guinea) for detailed sampling. (3) The outer bark is easy to obtain and the ashed bark reliably indicates Au concentrations in the substrate. (4) The root system reaches at least 4 m depth, allowing greater penetration than surface soil samples, which is important in volcanic terrains where geochemical targets may be buried by post-mineralization volcanic eruption or debris flows. (5) The areal distribution of the root system samples a large volume of soil (ca. 100 m 3), which reduces the nugget effect for Au. (6) The ease of sampling and low weight of bark reduces the time and cost over soil surveys, for example 6 minutes per site compared with 15 minutes per 1 m deep soil. Bark can be ashed in the field, 200–500 samples in 2 to 4 days, then shipped for multi-element (Au, As + 32 elements) instrumental neutron activation analysis (INAA). Field tests on Simberi and Lihir Islands, PNG, show that biogeochemical surveys have a high level of reliability for identification of prospects.

A comparison of lithogeochemical and biogeochemical patterns associated with gold mineralization in mountainous terrain of southern British Columbia

Analyses of rock and tree tissue samples collected from an area surrounding gold mineralization at the inactive Carolin mine show geochemical distribution patterns with some striking similarities and significant differences. Lithogeochemical sampling outlines a zone, several hundred meters across, in which hydrothermally altered rocks are enriched in Na and depleted in K and Ba. Within this zone lies a 40 m wide area where the rocks are enriched sporadically in Au and As. The Au, As, and Na biogeochemical halos outlined by twigs and needles of the most common tree in the survey area, Pacific silver fir (Abies amabilis), are significantly larger in areal extent than the respective lithogeochemical halos of these elements. This is a result of physical and chemical downslope dispersion of these elements in the colluvium and ground water. Differences in the biogeochemical and lithogeochemical patterns of Ba and Cr are attributed to the availability of these elements to the plant roots: in the hydrothermally altered rocks, Ba and Cr are more readily released from the crystal structure of such minerals as sericite and fuchsite than in the nonaltered rocks where these elements are most likely contained in K feldspar and chromite. This comparative study indicates that the biogeochemical method is a valuable approach to gold exploration in the mountainous terrain of British Columbia, because trees can integrate and amplify the geochemical signatures of rocks, surficial deposits, and ground water and give rise to large and intense anomalies derived from narrow zones of mineralization. Sampling and analysis of tree tissues is a cost-efficient method to identify areas of metal enrichment. At the Carolin mine, reconnaissance-level sampling at a density of a few trees per square kilometer would have been sufficient to identify the area of anomalously high Au, As, and Na concentrations. Reconnaissance biogeochemical surveys at this sample density in rugged terrain may assist in identifying valleys hosting mineralization that subcrops beneath a veneer of surficial deposits, and thereby, provide a focus for followup prospecting by lithogeochemical or other methods of exploration.

Platinum group metals in common plants of northern forests: developments in analytical methods, and the application of biogeochemistry to exploration strategies

Abstract All platinum-group metals (PGM) in ashed plant tissues, from an area of platinum mineralization in Saskatchewan, have been measured by neutron activation analysis of a NiS fire assay bead. Concentrations of up to 1350 ppb (ng/g) Pd, 880 ppb Pt, 49 ppb Rh, 37 ppb Ru, 24 ppb Ir, and 15 ppb Os occur in ashed twigs of black spruce ( Picea mariana ), indicating that the ratios of PGM uptake are about the same as those occurring in the bedrock. Plants growing on drift-covered diabase, known to have about 100 ppb PGM, contain up to 77 ppb Pt in ash, demonstrating the potential value of biogeochemical methods in helping to delineate platiniferous zones. Twigs of black spruce, jack pine, and labrador tea appear to be the optimum sample media in this environment. A rapid multi-element neutron activation analysis by direct irradiation of tissue permits measurement of 0.05 ppb Ir in dry material, or 2 ppb Ir in ashed samples. In view of the normally very low concentrations of Ir in plants, any detectable Ir probably indicates enrichment of PGM in the substrate. Comparison of several wet-chemical analytical methods indicates that the optimum (cost-effective) technique for detecting 1–2 ppb Pt, Pd, or Rh in 2-g samples of ash is by Te co-precipitation (following fusion and dissolution), and analysis by ICP-MS with sample introduction by electrothermal vaporization. However, care must be taken to ensure complete dissolution of all PGMs in the ash.

Botanical Exploration for Minerals in the Humid Tropics

Geobotanical and biogeochemical methods of prospecting for minerals have been little used in the humid tropics by comparison with temperate and boreal zones where these techniques were first developed. The reasons for this are discussed and the few published case histories available for the tropics are reviewed. Examples from south-central Africa, southern Asia, the Malay Archipelago and New Caledonia are used to illustrate the principles, practice and limitations of botanical reconnaissance methods for mineral exploration. The future potential of these methods for further exploration in the humid tropics is assessed.