Attachment_-_Statement_of_Work_1.pdf

Statement of Work

Lu-Hf and Sm-Nd and Pb isotope analyses of whole rocks and garnet

I. General information

A. Introduction

The USGS Geology, Energy, and Minerals Science Center requires Hf, Nd, and Pb isotope measurements of whole rock and mineral aliquots. These new isotopic data are essential for determining the melt sources of igneous rocks and constraining the timescales of deformation and metamorphism associated with magmatic activity. These data will support two MRP projects focused on the regional tectonic framework of the southern Appalachian Mountains and the

Precambrian bedrock of the Midcontinent and Intermountain West regions.

B. Background

Accurate tectonic reconstructions of terrane histories hinge on high-quality isotopic data that can be readily integrated with up-to-date geologic maps and modern geochronology. Tectonic models built on this foundation provide the strongest framework for developing prospectivity assessments for critical mineral resources. However, significant knowledge gaps remain in our understanding of the tectonic histories of the southern Appalachian Mountains and the

Precambrian bedrock of the Midcontinent and Intermountain West regions. Two new MRP projects aim to bridge these gaps by collecting new isotopic data from whole-rock and garnet aliquots to firmly link the deformation, magmatic, and metamorphic histories of these terranes in space and time.

Whole-rock Sm–Nd, Lu–Hf, and Pb isotope data will be used to determine the age and composition of the source regions of igneous rocks in these terranes. The Sm–Nd and Lu–Hf isotopic compositions of accessory minerals (e.g., garnet) will be used together to constrain the timing and duration of magmatic and metamorphic processes.

C. Scope

Whole-rock and accessory mineral Lu–Hf and Sm–Nd isotope analyses will be performed using isotope dilution. This process includes the acid digestion of accessory mineral and whole-rock aliquots in high-temperature pressure vessels (Parr type). The resulting solutions will be spiked with enriched 149Sm–150Nd and 176Lu–180Hf isotope tracers and then purified using cation-exchange column chromatography. The Pb isotope compositions of a subset of samples will be measured following digestion and purification by cation-exchange column chromatography. The isotopic compositions of the purified solutions will be analyzed using a multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS).

We require the following analyses:

• 6 whole rock analyses of Sm-Nd by isotope dilution and Pb isotopes for isotope concentration.

• 20 whole rock analyses of Lu-Hf and Sm-Nd isotopes by isotope dilution.

• 8 garnet aliquot analyses for Lu-Hf and Sm-Nd isotopes by isotope dilution

• 4 garnet aliquot analyses for Sm-Nd isotopes by isotope dilution, following H2SO4 treatment.

• 26 samples ground in agate for whole rock isotope work.

II. Work Requirements

A. Technical Requirements

The contractor shall have demonstrated experience in Lu–Hf, Sm–Nd, and Pb isotope analyses of geologic materials, isotope dilution, garnet geochronology, and multi-collector mass spectrometry. This experience shall be evidenced by a publication record encompassing all of these areas. The contractor shall also have demonstrated experience applying H₂SO₄ treatment to garnet aliquots when necessary to remove phosphate minerals and improve the accuracy of garnet Sm–Nd isotope measurements.

The sample preparation, wet chemistry, and mass spectrometry must be performed by the contractor with demonstrated expertise, and may not be subcontracted to a third party.

Isotope measurements shall be performed using a multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) with a demonstrated record of consistent and accurate analyses of the JNdi (Nd) and JMC (Hf) isotopic standards.

B. Deliverables

The contractor shall provide the deliverables in a digital format. Raw data will be provided in

Excel Spreadsheet files. The corrected and final data for all samples shall be of publication quality and will be provided in a single Excel Spreadsheet. The contractor will also provide the measured values of the standard solutions analyzed with the unknowns during the isotope analyses.

III. Supporting information

A. Place of performance

Washington State University Radiogenic Isotope and Geochronology Lab (RIGL)

B. Period of performance

12-months from date of award.