A - GEOCHEMISTRY
APPLICATION OF MULTI-ELEMENT GEOCHEMISTRY TO
THE GENERAL PROSPECTION OF IRAN
1.Type of sampling
The strategic geochemical prospecting has been based on the stream sediment sampling method. The efficiency of this method has been tested and proved
in many different countries and climates and at present it appears to be the most suitable technique for regional reconnaissance.
The fine alluvium samples, collected wherever possible from the secondary drainage network, provides a good picture of the geochemical characteristics of the drained catchment area.
Using this stream sampling method, rather than soil sampling, it is possible to employ a looser sampling grid than would otherwise be feasible,
Preliminary experiments were carried out to determine the sampling grid in two regions known to contain mineralisations (W. SAKOWITSCH, 1976). On the basis of their results a density of 1 sample per 2 sq. km was found to be sufficient and satisfactory for the general reconnaissance programme envisaged in the contract.
2.Sampling method and preparation
The samples were collected from the actual stream bed, after preliminary positioning of the sampling points on aerial photo's, taking into account the various mapped geological formations. For this reason, the geochemical campaign had to follow the cartographic work in the time schedule.
The samples were taken from the gravels, commonly under the relatively thin cover of recent mud. Each sample weighed approximately 300 grams.
The samples were first dried in the sun, or in a few cases by a small fire protected by a bed of gravel in order to avoid any roasting. They were then broken up by hand, but not crushed, and sieved to a mesh of 0.125 millimetres. The fine particles were then quartered, using a Jones divider, thus constituting the sample to be submitted to analysis. The latter were then hermetically sealed into plastic bags to be sent to the laboratory, a duplicate sample being stored by Geometal in Tehran.
Each batch of samples was accompanied by a form giving for each sample ;
- its number (sequential order),
- the nature of the host rock (using a numerical code),
- the number of the topographical sheet at 1/50 000,
- its geographical coordinates, using the U.T.M. system.
The sample number is assigned from .a sequential, four-figure, sequential numbering system. These numbers are used to identify the samples in the later data processing. This system has been applied to the whole zone being studied by Geometal-B.R.G.M.. The same numbers are marked on the sample location maps at 1/50 000, forming part of each report, and on air photographs.
3.1.Reasons for the choice of multi-element analysis
Systematic multi-element analysis is implicitly involved in .any regional geochemical prospection campaign. This technique, which increases the range of analytical data for each sampling point, offers many different advantages