Statement_of_Work_1.pdf

US Geological Survey Statement of Work

1.0 INTRODUCTION

The USGS needs to acquire mineral separates of apatite and zircon from bulk bedrock samples and zircon U-Pb dates.

2.0 BACKGROUND

The USGS conducts regional geologic and metallogenic framework studies that yield insight to the formation distribution of critical mineral resources in the United States. The Kuskokwim mountains region in southwest Alaska is host to numerous critical mineral-bearing resources, yet the geologic setting of these resources remains enigmatic, hampering complete assessment. Mineral separations and isotopic dating set the stage for better understanding the age and spatial distribution of the rocks these resources.

3.0 SCOPE

Separation of apatite and zircon from bedrock samples requires access to and expertise in the use of crushing equipment (jaw crusher, disc mill, or similar), sieves, an isodynamic magnetic separator, and multi-stage gravimetric separation by some combination of water table and/or heavy liquids (>2.9 g/cc and >3.3 g/cc for apatite and zircon, respectively).

The scientific goals of this project require minimally destructive U-Th-Pb isotopic analysis of zircon, such that follow-up grain-by-grain analytical work is feasible. This requires in situ techniques, such as laser ablation inductively coupled plasma mass spectrometry, for measurement of 238U, 232Th, 206Pb, 207Pb, and 208Pb (at a minimum). Additionally, access and contemporaneous analysis with some combination of community and internal analytical standards must be used.

USGS personnel will provide bedrock samples broken into chunks (fist-sized or smaller) and weighing no more than 5 kg. We request that mineral separations be sent to USGS personnel upon completion, who will prepare and image zircon mounts, and then return to the vendor for subsequent U-Th-Pb isotopic analysis.

4.0 TECHNICAL REQUIREMENTS

The contractor shall have experience in all aspects of mineral separation and zircon U-Pb analysis and access to the required instrumentation as described above. Samples are igneous rocks, and at least 20-30 zircon grains per sample should be analyzed (sample quality and yield permitting).

6.0 DELIVERABLES

The contractor shall provide mineral separations for each sample as separate and labeled vials that, at a minimum, contain: apatite, zircon, “lights” from gravimetric separation, and the various amperage/tilt intervals from magnetic separations used. Leftover, unprocessed bulk rock material should be returned to the USGS.

Zircon U-Th-Pb data shall be made available as an Excel spreadsheet that contains raw and standardized measurements of 238U, 232Th, 206Pb, 207Pb, and 208Pb and calculated isotopic dates and associated uncertainties following community-established norms and best practices. A write-up of analytical methods and instrument operating conditions should be made available upon request.