A Hydrogeochemical Exploration Study at the Pebble Deposit, Alaska

A Hydrogeochemical Exploration Study at the Pebble Deposit, Alaska R.G. Eppinger D.L. Fey K.D. Kelley S.M. Smith S.A. Giles  

Keywords porphyry Cu, exploration, hydrochemistry, high resoiution iCP-MS, Aiaska 

Cations were determined by high-resolution inductively coupled plasma-mass spectrometry (HR-ICPMS), relatively new analytical instrumentation with a large dynamic range and detection limits (DLs) in the low (1-50) parts per trillion (ppt) for most elements. The exceedingly low DLs allow for recognition of elemental variations that are not possible with traditional analytical methods for water. 

In 2007, regional water samples were collected along with local waters where present, along an east-west soil transect across the deposit (46 samples). In 2008, these were augmented with 83 more water samples, mostly from ponds over and around the deposit area, for a combined total of 129 water samples (Fig 1). Pond sediments were collected as well and geochemical analysis is underway. 

As summarized by Lang et al. (2007), regionally, upright Jura-Cretaceous argillite, siltstone, and wacke of the Kahiltna terrane are cut by a diverse suite of intrusions that occupy a northeasttrending structural corridor, likely related to the crustal-scale Lake Clark translational fault. At Pebble, subalkalic granodiorite bodies (91-89 Ma satellites to the Kaskanak Batholith) appear to be genetically related to mineralization. 

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