SOW_RFI_140G0324Q0214_1.docx

US Geological Survey Alaska Science Center Statement of Work

1.0 INTRODUCTION

The USGS needs to acquire high-quality mineral separates of apatite and zircon from bulk bedrock samples, and complimentary zircon U-Pb isotopic 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 Alaska Science Center has launched a new project focused on the Kuskokwim mountains region in southwest Alaska and requires mineral separations, as well as zircon U-Pb dates, from collected samples. The separation of minerals such as apatite and zircon from bulk bedrock samples sets the stage for a myriad of subsequent analytical work (such as thermo- and geochronology), whereas new zircon U-Pb dates serve to fill a data gap of modern radiometric dates--key to understanding the geological evolution of the area, episodes of magmatism, and unraveling possible ages of mineral deposits.

3.0 SCOPE

Separation of apatite and zircon from 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 ASC 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 APPLICABLE DOCUMENTS N/A

5.0 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.

7.0 PERIOD OF PERFORMANCE

From date of award to December 31, 2029