Gold distribution in the Archean Tanzanian Craton: Evaluating the effects of intracrustal differentiation

This study evaluates the vertical distribution of gold in the continental crust. Implementing a recently published method by Pitcairn et al. (2006a) for the chromatographic separation of gold from acid-digested rocks using diisobutyl ketone (DIBK), followed by analysis using standard addition inductively coupled plasma mass spectrometry (ICP-MS), high- and low-grade metamorphic rocks of the Tanzanian Craton, representative of the lower and upper crust, respectively, are analyzed to determine the distribution of gold in the crust. Greenstone belt basalts have the highest gold concentrations (ave.=60 (+193/-19) ng/g), followed by greenstone belt andesites (ave.=1.4 (+3.6/-0.6) ng/g). The lowest concentrations are observed in granulite-facies lower-crustal xenoliths (ave.=0.4 (+1.0/-0.1) ng/g). Gold is incompatible in silicates and can partition into hydrothermal and/or magmatic fluid during high-grade metamorphic dehydration reactions or partial melting, particularly if sulfides break down during these processes. Rise of buoyant mobile phases may explain the depletion of gold in the lower crust

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead