麻豆传媒

The Beaver Dam deposit is a metaturbidite-hosted mesothermal gold deposit, consisting primarily of slate with subordinate metagrewacke, and bedding-parallel auriferous quartz veins which contain variable amounts of carbonate. The purpose of this study is to use a whole rock lithogeochemistry approach on a large number of samples to determine whether there are geochemical and spatial correlations between hydrothermal alteration and gold mineralization. A portable X-ray fluorescence (XRF) spectrometer was used to analyze over 5000 samples. Each sample consists of pulps of drill core sampled at one meter intervals irrespective of lithology, quartz veins, or alteration. These samples were collected from over 50 drill holes within and surrounding a mineralized zone of the property with an overall strike length approximately 140m and 50m across strike. A set of 10 samples was reanalyzed 10 times each to ensure the reproducibility of the data. A subset of 30 samples was analyzed by ICP-MS to test the accuracy of the XRF spectrometer. The ICP-MS data was plotted against the XRF data to visually assess the accuracy of the XRF data. Most elemental plots created linear trends with a slope close to or equal to one.

The coarser clastic metasedimentary rocks are dominated by silica which dilutes other major and trace element concentrations, but are enriched in denser detrital minerals such as zircon. In contrast, the finer grained rocks are relatively depleted in silica and enriched in elements reflecting higher concentrations of micas and clays (eg. K, Rb, Ba) and the redox sensitive transition elements (Ti, V, Cr). Bivariate plots of V vs. Ti, V vs. Cr, and Ti vs. Cr show very good correlation (R2=0.85). These plots characterize the broad lithological groups, including quartz veins with concentrations approaching the origin, sandstones having lower relative concentrations of these elements, and slates having higher concentration of these elements. The very good correlation of these elements and distribution of concentrations likely reflect the general immobility of Ti, V, and Cr during hydrothermal alteration. When plotted against Ti and V, samples with elevated Mn and Ca concentrations likely reflect carbonate associated with quartz veins or naturally occurring in the host rock. Plots of K, Rb, Ba, and Sr vs. Ti and V show good correlation indicating that there is little to no mobility of alkali and alkaline elements. Of other elements plotted against the immobile elements, a small proportion of samples show slight elevations in As and Zn concentrations, suggesting these were introduced during alteration. However, when plotted against Au, As and Zn show a very weak correlation, and therefore may not have been introduced into the deposit at the same time as the gold. The nature of the sampling protocol of this study (which was taken at 1 m intervals down each drill core, conducted irrespective of lithology, quartz veining, or alteration) may have had an effect on the reliability of this data, and is responsible for the apparent mixing zone between lithological groups. The average of the fine fraction of gold from two analyses by fire assay was used to avoid the nugget effect having an effect in our results. The gold may have been introduced late or remobilized during late stage quartz veining. A plot of Au vs. V does show however, that the fine fraction gold is preferentially concentrated in the slates. To determine the spatial distribution, this information was generated into spatial sections, which confirm a very weak to non-correlation between alteration and gold on a scale greater than the 1 m sampling intervals.

Pages: 95
Supervisor: Michael Young