Separation of Uranium and Thorium for 230Th-U Dating of Submarine Hydrothermal Sulfides

Summary

The protocol describes a method to purify and separate the U and Th nuclide in submarine hydrothermal sulfide sample with Fe co-precipitation and extraction chromatography for ²³⁰Th-U disequilibrium dating.

Abstract

The age of a submarine hydrothermal sulfide is a significant index for estimating the size of hydrothermal ore deposits. Uranium and thorium isotopes in the samples can be separated for ²³⁰Th-U dating. This article presents a method to purify and separate U and Th isotopes in submarine hydrothermal sulfide samples. Following this technique, the separated U and Th fractions can meet measuring requirements by multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS). The age of the hydrothermal sulfide sample can be calculated by measuring the present-day activity ratios of ²³⁰Th/²³⁸U and ²³⁴U/²³⁸U. A super clean room is necessary for this experiment. Cleaned regents and supplies are used to reduce the contamination during the sample processes. Balance, hotplate, and centrifuge are also used. The sulfide sample is powdered for analysis and less than 0.2 g sample is used. Briefly, the sample is weighed, dissolved, added to ²²⁹Th-²³³U-²³⁶U double spike solution, Fe co-precipitated, and separated on an anion-exchange resin extraction column. Approximately 50 ng U is consumed for ²³⁰Th-U dating of sulfides sample by MC-ICPMS.

Introduction

Submarine hydrothermal sulfides have been a steady source of metals like iron, copper, zinc and lead. They are also seen as economically viable resources of silver and gold. The location and size of the deposits are a record of the history of hydrothermal venting on the seafloor. Dating of a hydrothermal sulfide can provide important information regarding the formation and alteration mechanism of the sulfide ore deposit, seafloor hydrothermal activity history, and growth rate of large sulfide deposits^1,2,3. ²³⁸U-²³⁴U-²³⁰Th disequilibrium datin....

Protocol

1. Preparing the sample, reagents, and containers

1. Clean the fume hood, hotplate and the balance room bench for the chemical experiment with sprayed alcohol or ultrapure water.
2. Prepare sub-boiled acids (2 M HCl, 8 M HCl, 7 M HNO₃, and 14 M HNO₃), clean beakers and any apparatus before sample processed.
   NOTE: Sulfide samples presented in this study were collected from newly discovered hydrothermal zones in the South Atlantic. Approximately 60 mg of powdered sample was used.......

Discussion

Some critical steps must be followed to ensure success of this protocol. Ensure that all operations are carried out in clean chemistry room under fume hood with clean air circulation. Purify all regents in this process in advance and clean the apparatus before use. Dissolve the samples completely in the process of making the 7 M HNO₃ solution which is then loaded onto the 7 M HNO₃-conditioned resins. If there is any insoluble substance in the sample, it will be redissolved after drying. Additional i.......

Materials

Name	Company	Catalog Number	Comments
AG 1-X8 anion-exchange resin	BIO-RAD	140-1441	Separating rare elements
Ammonia solution	Kanto Chemical CO., INC.	1336-21-6	Reagent
Glass vials	BOTEX	None	Sample collection
Hydrochloric acid	Sinopharem chemical reagent Co. Ltd	7647-01-0	Reagent
Hydrofluoric acid	EMD Millipore CO.	7664-39-5	Reagent
Neptune Plus	Thermo Fisher Scientific CO.	None	Apparatus
Nitric acid	Sinopharem chemical reagent Co. Ltd	7697-37-2	Reagent
Perchloric acid	Kanto Chemical CO., INC.	32059-1B	Reagent
Ultrapure water	Merck Millipore	None	Producted by Mill-Q Advantage systerm
Wipe paper	Kimberley-Clark	0123-12	Wipe and clean
2 ml vial	Nelgene	5000-0020	Sample collection
229Th-233U-236U spike	None	None	Reagent
7 ml PFA beaker	Savillex	200-007-20	Sample treatment
10 ml centrifuge	Nelgene	3110-1000	Sample treatment
30 ml PFA beaker	Savillex	200-007-20	Sample treatment