Hydrogeochemistry

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Why hydrogeochemistry?

Detecting of buried mineral deposits is a major challenge for the exploration industry. Exploration through cover has traditionally used drilling to sample the top of the units of interest and/or geophysical methods. For deposit types that don’t have well-defined geophysical signatures and regions too large to make close spaced grid drilling possible there have been limited exploration tools. Hydrogeochemical sampling of water to identify the composition of rocks with which it has interacted can help explore for buried mineral deposits.

Water preparation

Samples submitted for multi-element analysis need to be filtered, ideally at the time of collection and preserved with ultra-pure acids. This ensures only the elements in solution are measured, plus elements stay in solution during transport. If sample preparation is not able to be carried out prior to submitting, please identify the preparation methods required on the sample submittal form.

Filtering & acidification

ALS offer methods for filtering and/or acidification of water samples. Waters are filtered with a 0.45μm pore size paper to remove suspended particles. Samples for ME-MS14L™ should be acidified with nitric acid. Samples for Au-PATH14L™ should be acidified with aqua regia at the time of collection or by our WAT-PREP05 after submission to the lab.

Code	Description
WAT-PREP02	Filter water samples to <0.45um and acidify with nitric acid before analysis. Required when field filtering and acidification has not been performed.
WAT-PREP03	Filter water samples to <0.45um before analysis. Required when water has not been filtered before submittal.
WAT-PREP04	Acidify water samples with nitric acid before analysis. Required when samples have not been acidified before submittal
WAT-PREP05	Chemical treatment of water samples to desorb Au from containers before analysis.

Trace level multi-element analysis

Improvements in ICP-MS technology have brought detection limits to within an order of magnitude of those produced by high resolution HR-ICPMS instruments. An advantage to using traditional ICP-MS instrumentation for hydrogeochemistry is that they can accommodate higher total dissolved solids in samples reducing the need for sample dilution. The total dissolved solids of water samples that can be run by this method is 1% or lower.

ME-MS14L™

Our ME-MS14L™ method provides a suite of 50+ elements at super-trace detection levels. This method requires 50mL of water that is both filtered and acidified.

Code	Analytes & lower limits (μg/L)
ME-MS14L™	Au	0.002	Cu	0.1	Ni	0,2	Ta	0.01
	Ag	0.005	Fe	0.003 mg/L	P	0.005 mg/L	Te	0.01
	Al	3	Ga	0.05	Pb	0.05	Th	0.005
	As	0.05	Hf	0.005	Pd	0.005	Ti	0.2
	B	3	Hg	0.05	Pt	0.005	Tl	0.002
	Ba	0.05	In	0.01	Rb	0.01	U	0.002
	Be	0.005	K	0.01 mg/L	Re	0.002	V	0.05
	Bi	0.01	La	0,005	S	0.2 mg/L	W	0.01
	Ca	0.02 mg/L	Li	0.1	Sb	0.01	Y	0.005
	Cd	0,005	Mg	0.005 mg/L	Sc	0.01	Zn	0.5
	Ce	0.005	Mn	0.05	Se	0.05	Zr	0.02
	Co	0.005	Mo	0.05	Si	0.03 mg/L
	Cr	0.5	Na	0.01 mg/L	Sn	0.05
	Cs	0.005	Nb	0.005	Sr	0.05

Super trace gold & pathfinders

ALS has developed a new method for gold analysis in water samples that can determine gold concentrations down to 0.2ng/L. Due to the very low detection levels of this method only low TDS samples (<1%) can be analysed. The method also includes a group of select pathfinders that are useful for multiple style of gold mineralisation.

Method - Au-PATH14L™

ALS recommends sample preservation for the Au-PATH14L™ by a combination of hydrochloric and nitric acids. These acids effectively retain gold in solution as they provide both an oxidising agent and a ligand to complex with the gold. This method requires 50mL of water for the analysis.

Code	Analytes & lower limits (μg/L)
Au-PATH14L™	Au	0.0002-10	Co	0.005-1000	Pt	0.01-100	Tl	0.005-1000
Ag	0.005-100	Pd	0.005-100	Sb	0.02-1000	W	0.02-1000
As	0.2-1000

Anions & alkalinity

Anions and alkalinity of water samples need to be performed without acidification. These analytes are essential for carrying out charge balance calculations that are used to monitor analysis quality. They can be useful for identification of lithologies that have been in contact with the water, and some are even primary indicators of mineralisation, such as SO₄ in some environments.

MS14L-ANPH™

ALS offers an add-on method for anion and alkalinity measurement. These methods require 150mL of non-acidified water, for smaller volume samples please discuss with your local client service team. There is an option to determine speciated alkalinity and other parameters such as density. If any option other than those in the standard package are required, please contact ALS for more details.

Code	Analytes & lower limits (mg/L)
MS14L-ANPH™	Br	0.05	NO₃	0.005	pH	0.1 units	Conductivity	2 μS/cm
Cl	0.5	SO₄	0.5	TDS	3	Total Alkalinity	1
F	0.02

Rare earth elements in water

The determination of the rare earth elements in water can provide information useful to exploration applications where these elements are indicative of mineralisation.

Add-on rare earth element method (MS14L-REE™)

ALS offer analysis of 12 rare earth elements in water as an add-on method to ME-MS14L™. The method uses the same water as the ME-MS14L™ so an extra bottle is not required.

Code	Analytes & lower limits (μg/L)
MS14L-REE^TM	Dy	0.005	Gd	0.005	Nd	0.005	Tb	0.005
Er	0.005	Ho	0.005	Pr	0.005	Tm	0.005
Eu	0.005	Lu	0.005	Sm	0.005	Yb	0.005

Lead isotopes in water

Lead isotope composition will be retained in water that has taken Pb into solution from interaction with rocks and mineralisation. The change in the Pb isotopic ratios can indicate where Pb has been derived from host rocks or mineralisation.

MS14L-PbIS™

The method MS14L-PbIS™ is offered as an add-on to ME-MS14L™. The concentration of Pb²⁰⁴, Pb²⁰⁶, Pb²⁰⁷ and Pb²⁰⁸ is provided by this method.

Code	Analytes & lower limits (μg/L)
MS14L-PbIS™	Pb²⁰⁴	0.05
Pb²⁰⁶	0.05
Pb²⁰⁷	0.05
Pb²⁰⁸	0.05

Other isotopes in water

The sulphur isotopic composition of water can be very useful to identify the source of S in a water, either due to evaporative concentration in basins or from the breakdown of sulphide minerals. A determination of sulphide concentrations from the range of potential sources in a project area along with the values in water can identify the likely source of sulphur in a sample.

Various methods

Select isotopic methods for water samples are offered through the ALS partner, Queen's Facility for Isotope Research (QFIR). If there is an isotopic system you are interested in obtaining and it is not listed in our fee schedule, please contact ALS client services as they will be able to provide information on an extended range of methods.

Waters with high TDS

Any water sample that has a TDS concentration >1% is not suitable for super-trace methods as these methods have no dilution before analysis. When water has higher TDS alternative methods are needed.

ME-MS14™

The ME-MS14™ method is not suitable for high metal content samples or for environmental monitoring. For naturally occurring water with a TDS of between 1 and 6% the appropriate method is ME-MS14™. Any water with >6 % TDS will need to be analysed using method ME-ICP15 as samples are diluted before analysis as a necessary step to reduce interferences.

Code	Analytes & lower limits (μg/L)
ME-MS14™	Ag	0.06	Cu	1	Nb	0.05	Ti	10
	Al	0.02 mg/L	Fe	0.01 mg/L	Ni	2	Tl	0.05
	As	2	Ga	1	P	0.8 mg/L	U	0.05
	B	20	Hf	0.1	Pb	1	V	4
	Ba	0.5	Hg	0.5	Rb	0.3	W	0.2
	Be	0.3	In	0.3	Sb	0.1	Y	0.1
	Bi	0.1	K	0.6 mg/L	Sc	1	Zn	5
	Ca	0.2 mg/L	La	0.05	Se	10	Zr	5
	Cd	0.1	Li	10	Sn	0.4
	Ce	0.1	Mg	0.04 mg/L	Sr	0.4
	Co	0.1	Mn	1	Ta	0.2
	Cr	2	Mo	1	Te	10
	Cs	0.1	Na	0.3 mg/L	Th	0.05