Statement_of_Work.pdf

US Geological Survey Alaska Science Center

Statement of Work

1.0 INTRODUCTION

The USGS needs to acquire mineral separates from bulk rock samples, U-Pb geochronology on detrital zircons from sedimentary or metasedimentary samples, and U-Pb geochronology on zircons that crystallized in igneous rocks.

2.0 BACKGROUND

The USGS conducts research on regional geology and mineral resources. This involves making geologic maps of the area being investigated, and reconstructing the tectonic and metallogenic history.

Uranium-lead (U-Pb) zircon geochronology, or age determination, is one of the most important laboratory techniques used in this line of research. The samples submitted for mineral separation and two different types of geochronology analysis (i.e., detrital zircon ages and igneous crystallization ages) will help us elucidate the geologic evolution of bedrock samples from multiple regions of interest in

Alaska.

3.0 SCOPE

Mineral separates are first obtained by processing the rock samples that were collected in the field.

This involves crushing the rock, sieving the crushed sample, concentrating the mineral zircon using heavy liquids, and using a Frantz magnetic separator. The zircons are picked by hand under a microscope and mounted in epoxy. The U-Pb geochronology requires expertise in the use of laser ablation inductivity coupled plasma mass spectrometry (LA-ICP-MS), and access to appropriate lab facilities that meet the technical requirements described below. The age of each analyzed zircon is calculated from the analytical data, and analytical data and zircon ages are provided in Excel

Spreadsheet format.

4.0 APPLICABLE DOCUMENTS N/A

5.0 TECHNICAL REQUIREMENTS

The contractor shall have demonstrated experience in all aspects of mineral separation and igneous and detrital zircon geochronology using LA-ICP-MS methods. For each detrital zircon rock sample that is submitted, at least 100 individual zircons shall be analyzed. For each igneous crystallization age, at least 25 individual zircons shall be analyzed. Zircon analyses shall be conducted using a solid-state laser ablation (LA) system and either a quadrupole ICP-MS, a single-collector ICP-MS (high resolution and/or magnetic sector) or a multi-collector ICP-MS configured for precise isotope ratio measurement.

6.0 DELIVERABLES

The contractor shall provide deliverables in a digital report for each sample in Excel spreadsheet format, with both the raw and interpreted data included. The report shall include data from analytical standards. A publication-ready write-up of analytical methods shall be available (in digital form, as a Word document) to USGS on request. The contractor will ship the mineral separates, processed rock material, and any unprocessed rock to USGS.

7.0 PERIOD OF PERFORMANCE: January 1, 2022, to January 1, 2024