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FGV PROVENANCE AND SOURCE STUDIES AT NORTHWEST RESEARCH
PLEASE NOTE: ALL FGV SOURCE AND ARTIFACT STUDIES HAVE BEEN SUSPENDED THROUGH 2013
Due to some pressing laboratory commitments, we have suspended our FGV artifact and source provenance studies program for the entirety of 2013. We'll reevaluate the program at the end of the year and will post the results of our decision then. The extra time investment needed to successfully develop and implement our FGV program has outstripped our abilities to fully maintain all of our other lab services and we simply have to pull back from them for a while while we regroup and rethink.
For those of you who are actively engaged at the present time in FGV projects at the lab, no worries - we'll be finishing all current projects (but please don't wait too long to wrap things up).
INTRODUCTION
We have long been engaged in an active program of FGV (fine-grained volcanic rocks including basalt) source identification and trace element characterization studies in the Tahoe and Lassen national forest regions of California and have also widened our source coverage in recent years to include a limited number of other selected sources in Oregon, Nevada, Utah, Idaho, Arizona, Washington, and British Columbia. For more information about the FGV sources and characterization methods in general, see the links to the left.
Please note that we have no plans to further expand our FGV source coverage to significant new geographic areas, either in new states or in states in which we are already working. We have limited laboratory resources and it appears that our current areas of geographic source coverage will keep us quite busy for many more years.
We have also discontinued any further basalt and FGV characterization studies in Hawaii, southern Arizona, and any other locations not covered in our current FGV and basalt source catalog. Either these studies have not proven to be particularly productive (as in the Phoenix Basin or in southern California), or, as in the case of Hawaii, a local facility (University of Hawaii at Hilo) has developed the necessary resources for local basalt characterization studies.
WHAT IS AN FGV?
We use the term FGV - fine-grained volcanic material - to encompass a variety of different volcanic or igneous rocks that are used used for the manufacture of prehistoric stone tools. These rock types most often include basalts, andesites, rhyolites, and dacites. However, the classification of volcanic rocks is not a straightforward exercise and is done using a combination of chemical and textural or petrographic attributes. In short, it's simply not possible to reliably determine the correct rock type for volcanic materials using only visual or trace element characteristics. A dark, fine-grained rock, for example, might be basalt, rhyolite, dacite, shale (a metamporphosed sedimentary rock), or it might be something completely different. Because of this, we've adopted the FGV term in order to simply sidestep the need for accurate classification terminology.
For more basic information about the often-confusing topic of rock classification schemes, take at look at the Wikipedia entry for igneous rocks.
Fortunately, for all practical purposes in trace element provenence studies of FGV's, it doesn't matter if the material being tested is a basalt, an andesite, a rhyolite, or is some other type of volcanic rock. The key characteristics are that the the lithic material being tested is fine-grained, has no large phenocrysts or inclusions that can't be avoided by the X-ray beam (these are a different composition than the fine-grained matrix in which they occur), and is volcanic in origin. Geochemical sources must also be relatively homogeneous in their trace element composition and must also be chemically distinguishable from other regionally-available FGV sources (something that must be determined pragmatically through the geochemical analysis of multiple samples from potential sources).
BUT WAIT ... THERE'S MORE!
Although we have suspended our FGV studies program until further notice, we'll continue work on the FGV source catalog and will eventually be adding (1) An introduction to the basics of FGV provenance investigations at the lab, (2) FGV regional source maps, (3) Google map locations of selected FGV sources, and (4) Adobe Acrobat (PDF) source descriptions of the geochemical sources that are included in the laboratory FGV source reference comparative database.
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