Walker Lake Research Articles

Consistent geologic areas for epithermal gold-silver deposits in the Walker Lake Quadrangle of Nevada and California; delineated by quantitative methods; reply

Consistent geologic areas for epithermal gold-silver deposits in the Walker Lake Quadrangle of Nevada and California; delineated by quantitative methods; reply

Consistent geologic areas for epithermal gold-silver deposits in the Walker Lake Quadrangle of Nevada and California; delineated by quantitative methods; discussion

Consistent geologic areas for epithermal gold-silver deposits in the Walker Lake Quadrangle of Nevada and California; delineated by quantitative methods; discussion

A new multidimensional scaling technique based upon associations of triple objects—Pijk and its application to the analysis of geochemical data

A new multidimensional scaling (MS) technique, referred to as the Pijk model, is formulated on the basis of associations among triple objects (samples or variables), instead of pairs of objects as used in the usual MS methods, such as factor analysis. The computational scheme provided for this method is the reduction of an original problem to a standard eigenvalue-eigenvector problem. The major goal of the technique is simplification and reduction of data structures and the rescaling of original objects into a new and reduced space, so that patterns and relations of the original objects can be conventiently examined in two-dimensional “factor” plots. The Pijk method is illustrated and tested by using a set of geochemical data related to the epithermal gold and silver vein deposits in the Walker Lake quadrangle of Nevada and California. The characteristics of element associations suggested in the Pijk analysis are consistent with field observations. A preliminary comparison between the new method and the ordinary factor analysis also is made on the basis of the same data set. Results are encouraging in that analysis by the Pijk model captures triple-object associations that might be missed by the ordinary factor analysis which considers only pair-variable correlations

Indicator principal component kriging

An alternative to multiple indicator kriging is proposed which approximates the full coindicator kriging system by kriging the principal components of the original indicator variables. This transformation is studied in detail for the biGaussian model. It is shown that the cross-correlations between principal components are either insignificant or exactly zero. This result allows derivation of the conditional cumulative density function (cdf) by kriging principal components and then applying a linear back transform. A performance comparison based on a real data set (Walker Lake) is presented which suggests that the proposed method achieves approximation of the conditional cdf equivalent to indicator cokriging but with substantially less variogram modeling effort and at smaller computational cost.

Geology-exploration endowment models for simultaneous estimation of discoverable mineral resources and endowment

A new type of model, referred to as a geology-exploration endowment model, is proposed in this paper. These models differ from conventional ones in that they simultaneously estimate discoverable mineral resources and endowment by extracting and utilizing geoscience information from both geological features and exploration factors. Geological measurements describe mineral endowment, while exploration variables describe the completeness of exploration, and together, they explain discoverable resources. Without incorporation of exploration factors to geological-endowment models, the estimation of endowment is generally biased. This paper presents two variations of such hybrid nonlinear models: Poisson-logistic (PL) and exponential-logistic (EL) for estimation of number of mineral deposits or prospects based upon the Arps and Roberts' discovery process model and assumptions of endowment distributions. The PL model is obtained by assuming that endowment follows a Poisson distribution and that the probability of mineral occurrences (≥ 1) is a logistic function with geological arguments. The EL model is derived similarly, except that endowment is assumed to be exponentially distributed. The PL model is demonstrated on both a synthetic example and a case study of epithermal gold-silver vein deposits in the Walker Lake quadrangle of Nevada and California. A map containing the estimated numbers of gold-silver mineral occurrences potentially discoverable in the Walker Lake quadrangle is produced. The parameter estimates for the PL model based on the Levenberg-Marquardt iterative algorithm are validated by using several statistical measures, such as theT-statistic, Box's bias, and goodness of fit. Both a synthetic example and a case study suggest that the Box's bias measure is useful for validation of the nonlinear estimates.

Consistent geologic areas for epithermal gold-silver deposits in the Walker Lake Quadrangle of Nevada and California; delineated by quantitative methods

This paper reports initial research on a quantitative methodology for the delineation of consistent geologic areas as exploration target areas or favorable resource areas for epithermal gold-silver deposits. Important features of the methodology include (1) the use of a genetic model to structure information and to guide the analyses of geodata; (2) the identification of recognition criteria for heat source, the critical genetic factor selected for epithermal gold-silver deposits; (3) the enhancement of geodata using sample and variable weighting in selected multivariate statistical analyses and using two-dimensional Fourier transformations, filtering, and coherency analysis in the frequency domain for selected data; (4) the use of a control area to develop relationships useful in synthesizing information variables from the basic geodata (geochemistry, hydrothermal alteration, magnetism, gravity, structure, and lithology) that capture jointness effects; (5) the optimum cutting of each information variable to yield anomalies; and (6) the resolution of multiple information anomalies to probability anomalies for heat source by a two-stage multivariate logistic analysis. The methodology is demonstrated on the Walker Lake quadrangle of Nevada and California, a region known to have gold-silver deposits. This demonstration produced a map showing the consistent geologic areas. Thirty-two of these consistent geologic areas were selected as exploration target areas for epithermal gold-silver deposits. One of these target areas, located at Windmill, is shown in greater detail, revealing its magnetic, gravitational, geochemical, and structural anomalies.

Change in the size of Walker Lake during the past 5000 years

In 1984, a 12-m sediment core (WLC84-8) was taken from the deepest part of Walker Lake. Samples of the core were analysed for diatoms, pollen, carbonate mineralogy, magnesium content, δ 18O and δ 13C values of the total inorganic fractin, δ 18O and δ 13C values of Limnocythere ceriotuberosa, δ 13C values of the total organic fraction, grain size, and magnetic susceptibility. The data indicate that Walker Lake became shallow and probably desiccated between ⩾5300-4800 and 2700-2100 yr B.P.. Each of the organic and inorganic proxy indicators of lake size discussed in this paper was useful in determining the presence of the shallow-lake intervals. However, none of the indicators was useful in determining the cause of the shallow-lake intervals. Instead, the types of fish living in Walker Lake prior to 1940 were used to demonstrate that shallow-lake intervals resulted from diversion of the Walker River and not from climatic aridity. Major changes in mineralogy and magnesium content of carbonates and major changes in diatom populations with time were found to be a function of the chemical evolution of Walker Lake combined with changing lake size. The stable isotopes of oxygen and carbon were found to be good indicators of lake volume changes. A lake-level record for Walker Lake constructed from stable-isotope data was found to be similar to a lake-level record constructed using tufa and tree-stump data. Both records indicate relatively high lake levels between 4800−2700 yr B.P., at 1250 yr B.P., and within the last 300 yr. Substantial declines in lake level occurred ∼2000 and ∼1000 yr B.P.

Timing of the last highstand of Lake Lahontan

Radiocarbon and uranium-series ages of a variety of materials from the Lahontan basin indicate that the last highstand lake occurred between 14 500 and 13 000 yr B.P. Although few in number, existing radiocarbon and uranium-series age data also indicate that lakes in the western Lahontan subbasins were small or moderate in size between 30 000 and 25 000 yr B.P. Existing data do not support the conclusions of Bradbury et al. (1989) who did not find evidence of a 14 000±yr B.P. highstand lake in the sediments of the Walker Lake subbasin. These data also do not support the existence of a highstand lake in the Walker Lake subbasin between 30 000 and 25 000 yr B.P.

Limnology of Walker Lake and comparisons with other lakes in the Brooks Range, Alaska (USA)

Limnology of Walker Lake and comparisons with other lakes in the Brooks Range, Alaska (USA)

Quantitative analysis of anomalous sources and geochemical signatures in the Walker Lake quadrangle of Nevada and California

A new quantitative transportation model for geochemical elements in stream sediment samples is proposed and used to estimate mineral sources of anomalous concentrations and to adjust both location and concentration for the transportation effect. Subsequent to transportation analysis, data on 14 geochemical elements in the Walker Lake quadrangle are analyzed for geochemical signatures for three types of mineralization environments: epithermal gold-silver deposits, porphyry-skarn copper deposits, and a mixed occurrence. Geochemical signatures are analyzed using a multidimensional scaling method referred to as the p ijk model, which is a factor-like model generalized to include nonlinear associations, as well as linear, among triple variables (elements). A result of this analysis is that Pb is the best indicator for epithermal gold-silver mineralization, Mo and Zn for mixed mineralization, and Cu for porphyry-skarn mineralization.

Subdividing consistent geologic areas by relative exceptionalness of additional information; methods and case study

Mineral exploration or resources appraisal commonly employ geoscience concepts and available geoscience information to delineate subareas of special interest, such as geochemical and geophysical anomalies, exploration targets, metallogenic units, and favorable resource areas. These subareas may be thought of as being homogeneous with regard to the information and concepts used to delineate them and are here referred to as consistent geologic areas. The further subdivision of these areas into drilling targets or study areas based upon additional geoscience information is a task with which some geologists must deal. This paper develops an objective, quantitative methodology for further subdividing consistent geologic areas by the delineation of geologic heterogeneities. This methodology employs the principle of relative exceptionalness to identify locations that exhibit exceptional variation in normalized scores of geologic factors. The methodology is demonstrated on the Walker Lake quadrangle of Nevada and California, an area which contains epithermal gold-silver deposits.

Impacts of late Quaternary fluctuations in water level on the accumulation of sedimentary organic matter in Walker Lake, Nevada

Walker Lake, a terminal saline lake in western Nevada, has experienced major fluctuations in its water level due to changes in regional climate and river diversions during the late Quaternary. Change in the degree of preservation of sediment organic matter has accompanied the lake level fluctuations, and changes in the biotic sources of organic matter to the lake sediments have occurred in response to the climate changes and water diversions. The record of these events has been studied using organic matter C/N ratios and carbon isotope contents and employing molecular compositions of geolipids extracted from the sediment. Modern sediments contain mostly lake-derived organic matter which has been altered by microbial reworking. Decreases in the degree of preservation of organic matter indicate lake lowstands. Increases in the proportion of land-plant components in sediment organic matter also indicate lowstand conditions.

Organic geochemistry and brine composition in Great Salt, Mono, and Walker Lakes

Samples of Recent sediments, representing up to 1000 years of accumulation, were collected from three closed basin lakes (Mono Lake, CA, Walker Lake, NV, and Great Salt Lake, UT) to assess the effects of brine composition on the accumulation of total organic carbon, the concentration of dissolved organic carbon, humic acid structure and diagenesis, and trace metal complexation. The Great Salt Lake water column is a stratified Na-Mg-Cl-SO 4 brine with low alkalinity. Algal debris is entrained in the high density (1.132–1.190 g/cc) bottom brines, and in this region maximum organic matter decomposition occurs by anaerobic processes, with sulfate ion as the terminal electron acceptor. Organic matter, below 5 cm of the sediment-water interface, degrades at a very slow rate in spite of very high pore-fluid sulfate levels. The organic carbon concentration stabilizes at 1.1 wt%. Mono Lake is an alkaline (Na-CO 3-Cl-SO 4) system. The water column is stratified, but the bottom brines are of lower density relative to the Great Salt Lake, and sedimentation of algal debris is rapid. Depletion of pore-fluid sulfate, near l m of core, results in a much higher accumulation of organic carbon, approximately 6 wt%. Walker Lake is also an alkaline system. The water column is not stratified, and decomposition of organic matter occurs by aerobic processes at the sediment-water interface and by anaerobic processes below. Total organic carbon and dissolved organic carbon concentrations in Walker Lake sediments vary with location and depth due to changes in input and pore-fluid sulfate concentrations. Nuclear magnetic resonance studies ( 13C) of humic substances and dissolved organic carbon provide information on the source of the Recent sedimentary organic carbon (aquatic vs. terrestrial), its relative state of decomposition, and its chemical structure. The spectra suggest an algal origin with little terrestrial signature at all three lakes. This is indicated by the ratio of aliphatic to aromatic carbon and the absence of chemical structures indicative of the lignin of vascular plants. The dissolved organic carbon of the Mono Lake pore fluids is structurally related to humic acid and is also related to carbohydrate metabolism. The alkaline pore fluids, due to high pH, solubilize high molecular weight organic matter from the sediments. This hydrophilic material is a metal complexing agent. Despite very high algal productivities, organic carbon accumulation can be low in stratified lakes if the anoxic bottom waters are hypersaline with high concentrations of sulfate ion. Labile organic matter is recycled to the water column and the sedimentary organic matter is relatively nonsusceptible to bacterial metabolism. As a result, pore-fluid dissolved organic carbon and metal-organic complexation are low.

Biogenic magnetite in stromatolites. I. Occurrence in modern sedimentary environments

Abstract In this paper we report the occurrence of biogenic ultra-fine-grained, single-domain magnetite in both marine and non-marine modern stromatolitic environments. Magnetotactic bacteria were found associated with the microbial communities involved in the deposition of laminated sediments at Laguna Figueroa, Baja California, Mexico and carbonate stromatolitic nodules at Sugarloaf Key, FL, U.S.A. These bacteria and the ultra-fine-grained magnetite they produce have a profound effect on the magnetic properties of the sediments. The presence of this single-domain magnetite was detected using rock magnetic methods, while the morphology was identified by transmission electron microscopy. Examination by rock magnetic methods of microbial mats and laminated sediments from Solar Lake, Sinai, Guerrero Negro, Baja California, Mexico and Shark Bay, Australia, as well as stromatolites from Shark Bay and Clifton Lake, Australia, Bacalar Lake and Cuatro Cienegas, Mexico, and Walker Lake, U.S.A., indicate these localities contain single-domain magnetite. Biogenic magnetites of presumed bacterial origin have been extracted from Shark Bay mats, Walker Lake stromatolites and Bahama carbonates. These findings suggest that bacterial magnetites can be recognized as the tiniest trace fossil and may be found preserved in fossil stromatolites and laminated sediments.

Late Quaternary paleolimnology of Walker Lake, Nevada

Late Quaternary paleolimnology of Walker Lake, Nevada

Late Quaternary Chronology of Tufa Deposits, Walker Lake, Nevada

Walker Lake, a terminal desertic lake in Mineral County, Nevada, has fluctuated greatly in lake level throughout its long history due to changes in climate and drainage. In its Late Pleistocene high stand, Walker Lake formed the southernmost embayment of pluvial Lake Lahontan. Calcareous tufa and other shoreline deposits of Pleistocene and Holocene ages provide a valuable record of past lake levels. Studies of tufa morphology and stable isotope character, closely integrated with sedimentologic data, show great promise for elucidating the post-glacial climatic history of the Great Basin. Three prominent shoreline carbonate deposits below 1250 m have been studied in the field and with stable isotope and radiocarbon analyses. The oldest deposit (18,000 radiocarbon yrs B.P.) consists of massive, bowl-shaped tufa heads outcropping from conspicuous wavecut and fan-deltaic terraces. Three "bigheads" are covered by alluvial fan deposits, which in turn are coated by an "encrusting tufa" of 3 cm average thickness. This encrusting tufa, dated at 2150 yrs B.P. and exhumed during the historic drop in lake level, coats virtually every undisturbed boulder around the entire lake. The third deposit, a 2 mm "outer rind," coats the first two deposits and has modern pre A-bomb or A-bomb radiocarbon levels depending on sample elevation. The $$\delta^{13}C$$ values for the bighead deposits average $$3.41 \pm 0.10\%0$$, and the $$\delta^{18}O$$ values average $$-1.47 \pm 0.61\%0$$. The $$\delta^{13}C$$ and $$\delta^{18}O$$ values for the encrusting tufas average $$3.21 \pm 0.12\%0$$ and $$-0.68 \pm 0.25\%0$$, respectively, and the $$\delta^{13}C$$ and $$\delta^{18}O$$ values for the outer rinds average $$3.09 \pm 0.17\%0$$ and $$-0.10 \pm 0.34\%0$$, respectively. Isotopic paleotemperatures for the two Holocene deposits range from 27 to 35°C, the same as shoreline values measured in July and August. Our results indicate late Pleistene low stands below 1222 m circa 18,000 yrs B.P., a post-Pleistocene period of desiccation during which alluvial fans formed, another rise to 1250 m, another period of desiccation circa 2000 yrs B.P., a rise to the historic high stand of 1244 m and, since 1880, a drop to 1206 m.

Tritium hydrologic studies in four closed‐basin lakes in the Great Basin, U.S.A.1

Four closed‐basin lakes in the Great Basin (Lake Abert, Oregon; Mono Lake, California; Pyramid Lake and Walker Lake, Nevada) were analyzed for tritium (3H) in water samples collected in 1969, 1976, 1980, and 1981. In each case the tritium concentration increased to a maximum in the mid‐to late 1960s in response to fallout produced by nuclear weapons testing and then slowly decreased soon after the 1966 moratorium. The highest level attained was a function of the water residence time of the lake (i.e. shorter residence time corresponding to higher maximum tritium concentration), and the rate of decrease was slowest for lakes with longer water residence times. The residence time of tritium is less than the water residence time and depends strongly on the evaporative exchange of tritium with the atmosphere.A tritium hydrologic model was constructed in an attempt to constrain hydrologic properties such as evaporation rate, relative humidity, and the degree of homogeneity of the water column with respect to tritium. If evaporation rates determined from hydrologic balance are within 20% of the true rates, then the tritium input must be between 50 and 90% enriched over that calculated from data on tritium fallout in Portland rain. This enrichment is considerably reduced if the surface waters are on the average depleted by about 10% in tritium relative to the whole lake. Calculated mean relative humidities lie between 0.45 (Mono Lake) and 0.25 (Walker Lake). Calculated exchange velocities in the gas phase are between 17 and 27 m h−1, which corresponds to a mean wind speed of about 4 m s−1.

Sedimentary biomarker and isotopic indicators of the paleoclimatic history of the Walker Lake basin, western Nevada

Walker Lake, a terminal saline lake in western Nevada, has experienced major fluctuations in its water level due to changes in the regional climate during Quaternary times. As part of a paleo-climatological study of western Nevada, we have investigated organic matter δ 13 C and C/N values and lipid biomarker contents of sediments deposited at various periods over the past 150 thousand years of lake history. Surficial sediments from two cross-lake transects contain mostly lake-derived organic matter. Diagenetic losses of organic matter are evident in deeper sediments, and the proportion of aquatic and terrigenous organic materials changes in response to variations in preservational factors. Source identification of organic matter is complicated by the probability that Walker Lake has experienced desiccation at various times in its history which impacts the degree of preservation of organic substances.

Lake-level variation in the Lahontan basin for the past 50,000 years

Selected radiocarbon data on surficial materials from the Lahontan basin, Nevada and California, provide a chronology of lake-level variation for the past 50,000 yr. A moderate-sized lake connected three western Lahontan subbasins (the Smoke Creek-Black Rock Desert subbasin, the Pyramid Lake subbasin, and the Winnemucca Dry Lake subbasin) from about 45,000 to 16,500 yr B.P. Between 50,000 and 45,000 yr B.P., Walker Lake rose to its sill level in Adrian Valley and spilled to the Carson Desert subbasin. By 20,000 yr B.P., lake level in the western Lahontan subbasins had risen to about 1265 m above sea level, where it remained for 3500 yr. By 16,000 yr B.P., lake level in the western Lahontan subbasins had fallen to 1240 m. This recession appears synchronous with a desiccation of Walker Lake; however, whether the Walker Lake desiccation resulted from climate change or from diversion of the Walker River is not known. From about 15,000 to 13,500 yr B.P., lake level rapidly rose, so that Lake Lahontan was a single body of water by 14,000 yr B.P. The lake appears to have reached a maximum highstand altitude of 1330 m by 13,500 yr B.P., a condition that persisted until about 12,500 yr B.P., at which time lake level fell ≧100 m. No data exist that indicate the level of lakes in the various subbasins between 12,000 and 10,000 yr B.P. During the Holocene, the Lahontan basin was the site of shallow lakes, with many subbasins being the site of one or more periods of desiccation. The shape of the lake-level curve for the three western subbasins indicates that past changes in the hydrologic balance (and hence climate) of the Lahontan basin were large in magnitude and took place in a rapid step-like manner. The rapid changes in lake level are hypothesized to have resulted from changes in the mean position of the jet stream, as it was forced north or south by the changing size and shape of the continental ice sheet.

A pump sampler study of microdistribution in Walker Lake, Arizona, U.S.A.: a senescent crater lake

SUMMARY. 1. The seasonal microdistribution of physico‐chemical features and plankton were examined at close intervals in a high elevation (2493m) senescent crateri lake (1m deep) in the arid southwestern U.S.A.2. The protective volcanic rim and dense growth of provided highly stable thermal conditions throughout much of the year with the thermocline frequently in the top 30cm of the water column during the summer and dissolved oxygen typically <3.0mgl−1 in surface waters and <1.0mgl−1 below 50cm.3. The microdistribution of both phytoplankton and zooplankton was examined at close intervals (10cm) throughout the water column with the aid of a peristaltic pump.4. Aglaodiaptomus leptopus, along with Dinobryon sertularia and certain diatom species, were largely restricted to the top 30cm, while the colonial phytoflagellate, Pyrobotrys elongata and certain euglenoids were mostly located in the anaerobic lower strata.5. Cryptomonas obovata demonstrated subsurface maxima at various locations within the water column depending upon season.6. The distribution of plankton was also compared during daylight and darkness on one date.