We used samples from six Finnish ore deposits to evaluate the efficiency of sample pretreatment procedures — crushing, splitting and grinding — and to compare three analytical methods based on the atomic absorption determination of gold following: (1) classical lead fire assay (FA); (2) the aqua regia leach (AR) followed by Hg coprecipitation of Au; and (3) the sodium cyanide (NaCN) leach. Sample size used for the method comparison is 20 g. The Au deposits and ore types were: Suurikuusikko and Osikonma¨ki, refractory ores in which Au is associated with arsenopyrite and pyrite; Pampalo and Kutemaja¨rvi ores with metallic Au and Au tellurides; and Jokisivu and Pahtavaara ores containing coarse-grained metallic Au. After crushing, the samples were split into three parts, one of which was put aside into storage. Two splits were further divided into two subsamples which were ground to two grades of fineness (<0.03 and <0.06 mm). The four subsamples thus obtained were analysed for Au using the three analytical methods. Each determination was performed five times on each of the four subsamples. According to t-tests on the FA results of the two splits, crushing and splitting produced samples of equal Au content in all six cases. Grinding to a finer grain size gave a significant difference in Au results only for the Pahtavaara ore sample. If the FA results are assumed to represent 100% recovery of Au, we obtained greater than 95% recoveries for all but the Suurikuusikko sample (87% recovery) by the AR leach method. We also obtained recoveries of over 95% by the NaCN leach method for the Pampalo, Kutemaja¨rvi and Pahtavaara samples, whereas recoveries for the other three samples varied between 73 to 92%. The AR leach was also performed on 1-g samples and the NaCN leach on 250-g samples. For three of the ore samples, decreasing sample size from 20 g to 1 g did not cause a significant difference in the variance of the Au results. Increasing the sample size from 20 g to 250 g significantly improves the representativity of only the Pahtavaara sample. For the Kutemaja¨rvi, Pahtavaara and Jokisivu ores, a sample larger than 250 g is needed in order to obtain a precision equivalent to that for reference samples.

THIS book is an outgrowth of my doctoral dissertation at Harvard University. It is not a final report of investigation, nor does it presume to be the last word on hydrothermal ore-forming solutions.

A compilation of data on 78 elements in the nine groups of chondrites shows each to be isochemical with the exception of a few volatiles. With the exception of the most volatile elements, the groups have solar abundances to within a factor of two. The solar abundances and the chemical and physical properties of phases in the least-altered chondrites indicate formation by grain agglomeration in the preplanetary nebula.

Pre-existing crustal structures are important in localising strain related to the large-scale evolution of an orogeny. Rheological contrasts between basement blocks will also influence the degree and location of faulting and relative uplift. In northern Nevada, U.S.A., basement architecture in the form of early rifted continental margins, formed during Proterozoic extension, may dictate the subsequent structural geometry of overlying sedimentary sequences during large-scale compression (Figure 1a). Within the region of the Carlin gold trend, specific anticlinal fold and thrust geometries in the sedimentary rocks, involved in various orogenies up until the Laramide, may focus fluid movement and provide effective traps to the system, resulting in the unique gold endowment of the area. Most mineralisation is situated less than 100 m below the Roberts Mountain thrust, which defines the lower boundary of the sequence of deep-water sedimentary rocks that has ridden over both the basement and younger sedimentary layers.

Muntean et al. (2003) argue that the Carlin and Battle Mountain–Eureka (BME) gold trends (Figure 1b) correspond to reactivated normal faults that likely had their origins in Proterozoic rifting. Numerical modelling offers a way to test the basic hypothesis by which “steps”, relics of continental rifting, control the subsequent location of upper crustal faults and anticlinal structures during compression.