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Link to information on the groundwater geochemistry handbook by Angela Giblin

Groundwaters - Geochemical Pathfinders to Concealed Ore Deposits  

and free geochemical modelling software and useful references.

See also AIG Newsletter Article on Groundwaters

This page has numerous diagrams and takes a few minutes to download - please be patient.

 Why are groundwaters important for mineral exploration in  Australia as well as ELSEWHERE in the world?

The key reasons are:

New deposits are likely to be concealed by cover.

Groundwaters move through covered rocks.

Groundwaters react chemically with rocks in their path, collecting mobile components typical of the concealed rocks they have passed though.

 Geochemical groundwater analyses for exploration provide indications of:

Economically significant trace elements.

Major element relationships indicative of concealed rock types and alteration.

Concealed mineral assemblages may be determined by geochemical reaction modelling.  

Multivariate analysis and grouping of ground water constituents may define ore locations.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Commodity Trace Elements

 

If a target commodity is rare and it is chemically poorly reactive, for example Au,  then values determined, whether big or small, are GOOD.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

If a target commodity is not so rare, for example, copper, then big numbers are NOT necessarily good.  You need to consider solubility of target mineral (eg. Cu minerals) in the specific groundwater.  This depends upon other species present and their relative concentrations.

 

 

 

 

 

 

 

 

 

 

So knowing the chemistry of a groundwater, the amount of Cu that goes into a solution from a Cu mineral can be calculated.  The figure below compares measured concentrations of Cu in groundwaters with those calculated for a groundwater-rock system that includes oxidised Cu minerals.  Illustrated are seven samples in which the Cu content is high enough to conclude that Cu minerals are present in the vicinity.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Major Element Relationships

Exploration Applications:

Determine the presence or absence of concealed mafic or ultramafic rocks

Determine major zones of alteration

Mafic or ultramafic rocks may be identified by local elevations or depletions in groundwater Mg, expressed as a proportion of major cations (NMg) (normalised).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Geochemical Reaction Modelling

Exploration Applications:

Identify stable mineral assemblage in equilibrium with ground water.  Assumes no mineral is undersaturated and fluid is not supersaturated with respect to any mineral.
Mineral assemblage can be calculated for each groundwater at its theoretical state of true equilibrium; minerals so indicated characterise a groundwater.
Identify concealed aquifer rocks.

An example - Serpentinite minerals as indicators for Victorian gold deposits:

Serpentinite units in Cambrian greenstones believed to be hosts of gold later incorporated into structurally hosted Ordovician gold ores, (Crawford et al., 1996).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

An example - 

Identification of concealed aquifer rocks by determining what minerals control the compositions of a series of  ground waters:

Model groundwater from south of Stawell in Victoria.  The low salinity implies recent formation. Analyses of major elements gives:

pH             7

Ca2+        1.0        mg/L

Mg2+        1.2        mg/L

Na+           14        mg/L

K+            1.0        mg/L

Cl-             20        mg/L

SO42-        3.1        mg/L

HCO3-        5          mg/L

Al3+        0.19e-9    mg/L

SiO2(aq)  0.19e-9   mg/L

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Multivariate Analysis of Existing Geochemical Data

Using groundwater data from a Tennant Creek study, a clustering procedure based on groundwater concentrations of a suite of major and trace constituents delineates discrete zones that coincide with a general zone of high residual gravity.  

Variables analysed and used in the cluster analysis were:

Cu, Pb, Zn, U, Al, Fe, Mn, Ba, Co, Sr, Ni, As, Li, Si, V, Rb, 

Cs, NCa, NMg, NK, NSO4, Sc, F, Au, Mo, and Ge.

Clustering procedure was K-means clustering of Principal Component Scores 1, 2, 3, and 4

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Contact: Angela Giblin

email:  gib063@tpg.com.au

The handbook

Groundwaters - Geochemical Pathfinders to Concealed Ore Deposits

 may be downloaded from the following site:

http://www.em.csiro.au/news/publications.htm#groundwaters

Try right click and "Save Target As" option if you have download problems.

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Last modified: August 14, 2007