Comparative elemental and oxygen isotope geochemistry of jasperoid in the northern Great Basin; evidence for distinctive fluid evolution in gold-producing hydrothermal systems

Abstract

This comparative geochemical study of jasperoid in the northern Great Basin is based on 65 samples from 10 Carlin-type gold deposits and 22 similar but apparently barren hydrothermal systems. Multielement geochemistry coupled with oxygen isotope data indicate that hydrothermal fluids in barren and mineralized systems evolved in different ways, and that there are fundamental geochemical differences among the various gold-producing deposits of the area.Much of the variation in the jasperoid geochemical data can be explained in terms of seven abstract end-member components obtained through factor analysis. Three of these components (factors) dominate the results and are related to common products of alteration and mineralization in epithermal systems of the northern Great Basin. Element associations for these factors are: factor 1: TiO•, A12Oa, La, K20, Sr, Fe•Oa, Th; factor 2: Au, Ag, Sb, SiOn, As, Pb; and factor 3: W, B, V, Zn, Co, Au, CaO, Ni, Mn, Cu.Samples from barren systems are predominantly associated with high factor I loadings, whereas samples from mineralized systems are generally characterized by high loadings of factor 2 and/or factor 3. Factor I is related to residual, argillically altered, noncarbonate constituents in original host rocks. Factor 2 is related to hydrothermal silica (jasperoid) and is characterized by many of the so-called pathfinder elements used in Great Basin exploration. Factor 3, although characterized by a transition metal assemblage, is related to syngenetic inclusions of hydrothermal calcite within jasperoidal silica.High factor 2 loadings are associated with samples from the Windfall and Northumberland deposits but not with samples from other gold-producing systems in the study. Factor 3, on the other hand, is the dominant component in most samples from the Carlin, Gold Quarry, Maggie Creek, Pinson, and Preble deposits. It therefore appears that there are at least two geochemically discernible types of gold deposits in the northern Great Basin. These types are represented in this study by the Windfall deposit (factor 2) at one extreme and by the Gold Quarry deposit (factor 3) at the other. Other deposits, including Alligator Ridge and Tonkin Springs, are intermediate between these extremes. In this study, the hydrothermal geochemistry of the Jerritt Canyon samples is obscured by a chert-related compositional factor. Jasperoid samples from gold-producing ore deposits have filSO values ranging from 3 to 20 per mil, whereas jasperoid samples from analogous barren systems have fi•sO values ranging from 3 to 11 per mil. This indicates that at least some fluids in ore-related hydrothermal systems were relatively lsO rich compared to those in barren systems. Jasperoid samples having high •sO values invariably have high factor 3 loadings. The elemental and isotopic geochemistry ofjasperoid samples indicates that hydrothermal fluids in individual gold-producing systems of the northern Great Basin evolved in differentways. It appears that high CO• contents were a critical distinguishing ...

Geology and geochemistry of the Vantage gold deposits, Alligator Ridge-Bald Mountain mining district, Nevada

“…A regional study of the oxygen isotope compositions ofjasperoids in the eastern Great Basin (Holland et al, 1988) reports that jasperoids associated with Au deposits generally have 61sO values of 8 to 20 per rail, whereas barren jasperoids have lighter oxygen. All the values reported here fall within the productive range regardless of their proximity to ore or stratigraphic position, but Joana and Chainman jasperolds do not in general host even subore-grade mineralization.…”

Application of gas analysis of jasperoid inclusion fluids to exploration for micron gold deposits

“…Because jasperoid is commonly the most prominent outcropping rock in sediment-hosted micron gold deposits and because it is also found in other types of hydrothermal systems, considerable attention has been given to the possibility of discriminating between jasperoids from barren and mineralized micron gold systems. Most of these studies have concentrated on trace-element and isotopic characteristics (Holland et al, 1988;Nelson, 1990 ). Haynes and Kesler ( 1988 ) noted that fluid inclusion gas geochemistry could have some advantages in evaluation of jasperoids because the inclusion gases should be more homogeneously distributed than gold and other metals.…”

Geology, mineralogy, geochemistry, and geothermometry of Kelley Limestone jasperoids, Magdalena mining district, New Mexico

“…Theodore and Jones (1992) stated that gold concentrations in jasperoids are typically very spotty because sedimentary-hosted Au-Ag deposits along the Carlin trend of north-central Nevada contain jasperoids commonly showing insignificant gold concentrations in one sample and anomalously high concentrations in another sample only several meters away. Recent studies of jasperoids from the northern Great Basin also confirmed an extreme variability in elemental concentrations in suites of samples obtained from a single deposit (Holland et al, 1988). In addition, many of the sedimentary-hosted Au-Ag deposits along the Carlin trend and the Preble-Pinso-Getchell alignment show a zonation from distal carbonate veins, through mixed carbonatejasperoid veins, to jasperoid-only mineralized veins proximal to the deposits (Madrid and Bagby, 1988).…”