- NEW TARGETS FOR MINERAL EXPLORATION

 - KNOWN SHOWINGS THAT MERIT A DETAILED RE-EVALUATION

NEW TARGETS FOR MINERAL EXPLORATION

Cross-analysis of the different layers of information with Synarc™, a software tool developed by BRGM and ESRI, allows to produce synthetic documents and thematic maps which can be used for the selection of new exploration targets and adapted methodologies.

 - Examples of base layer data

 - Examples of Grid combination and analysis

 - Weight of evidence modeling

Examples of base layer data

Grid combinations, analysis

Au-Cu-Zn occurences Basement outcropping Au-occurences density	Au occurences favorability Basement outcropping Au-occurences density	Grid combination Au-occurences density and Basement outcropping

Weight of evidence modeling

	The underlying philosophy of weight of evidence modeling
Geology		Geology Faults

KNOWN SHOWINGS THAT MERIT A DETAILED RE-EVALUATIONKNOWN

Gold in shear zones

Fawarah, Gariat Avala, Mamilah, Aqiq Ghamid, Miha, Masan, Umm Mathierah, Ishmas Kabir, Bir Jabuah, As Suq/Haffirah cluster, Bir Tawilah Au, Jabal Mugherah, Ar Rjum Au, Jabal Guyan, Shignah, Samhah, Mangar An Nam, Jabal Hamick, Tayma, Azzeraib, Umm Lajj, Al Wajh, Selib, and Wadi Merjan.

Gold in shear zones associated with altered ultrabasic rocks

Hamdah, Ghadarah (also associated with syntectonic intrusions in the shear), Shiaila (idem), Umm Ash Shara, and Wadi Tulay.

Gold showings associated with intrusive bodies

Al Qoom, Aklyah, Al Habla, Al Qubbah, Simfan um Shieh, Bir Tawilah Au, An Najadi, Meshaeed, Wadi Shabaah, Al Habla, Makkah Road, Jabal Mawan, Umm Ash Shatton (dike), Wadi Unaybick (leucogranite), Ash Shaktalyah (subvolcanic), Murajib, and Billiwy (low-grade/large-tonnage).

Volcano-sedimentary deposits

Kuroko type

For supergene enriched residual gold: Rabathan, Shaib At Tare, Mulhal, Gehab, Lahuf, Jadmah, Farah Garan, Wadi Shugea, Al Jaufir (Wadi Shwas-Wadi Bidah belts), and Jabal Sayid gossan.

Polymetallic lens: Al Masane (gold anomalies around the deposit should be checked), Umm Ad Damar, Kutam, Umm Hijlan, An Nimar, Al Halahila, Baydan, Maadan-Mahawiyah, Gith Gath, Ash Shaib, Wadi Wassat.

In addition, the Afif, Shaib-Lamisah, and Samran districts contain Input and geochemical anomalies that were not checked, and gold gossans that have to be re-sampled.

Co-Bi bearing stockwork to be checked for gold at Ash Shizm.

Cyprus type

Jabal Mardah (Ni gossan).

Sedex type

Nuqrah, Umm Ar Rjum (Zn prospect), As Safra (pro-parte), Shaib Lamisah, Al Meddadah, Jabal Hamik, Gossan Hulayfah, Al Aqiq, Al Gharith (Au-Ag-Ba, Mn). The last two examples have a somewhat hybrid character, and a combination epithermal-sedex is possible.

Ni-Mo Black-Shale type

Wadi Qatan, As Siham gossans, Al Maham, Jabal Al Ma’zah, and Habdah.

Disconformity type

Dhaylan and Wadi Azhlan. In addition, most oil-bearing layers have a high base-metal potential, in particualr around salt diapirs in Mesozoic Cover Rocks. A re-examination of certain oil-well cores is to be envisaged.

Porphyry type

Musayna’ah (Cu-Au), Jabal Hamra (SW of Musayna’ah), Bari (polyphase polymetallic), As Safra (Cu-Au), Samrah, Arjah (Ag), Mo gossan near Afif SW, Al Lugata, and Jabal Ash Shuhaban.

Epithermal type

At Taybi, Umm Adh Dabah, Umm Hadid (Al Amar), Al Gharith (Ba-Mn-Ag), Asfar Al Hadawi (Ag-Ba-U), Al Himar (Mn-Au), As Safra (pro parte) and Umm Ash Shalahib (with a very low priority).

Ophiolitic chromites: Al Ays in particular for PGE

Banded basic-ultrabasic complexes: Wadi Kamal in particular for PGE

Zoned mafic intrusions: Lakatah (Fe-Ti), Jabal Jedair, Jabal Rugaan, Jabal Gharhabah: to be checked for PGE.

All descriptive elements of these showings can be found in the Occurrence table of the GISARABIA GIS.

Future work and perspectives

To improve the success of mineral-exploration work in the Kingdom, several ways are possible:

Optimize the selection of favorable areas through:

a better knowledge of mineralization models and

an enlargement of the GIS by integrating drill-hole data, and the addition of new data, such as remote sensing, geochemistry, radiometry, etc.

Provide new tools for delineating targets at the follow-up stage, for instance in-situ measurement of some parameters like mineralogy (PIMA), hydrogeochemistry, gases, etc.

Improve the analytical data for identifying those anomalies really indicating a mineralization; using, for example, selective extraction techniques or enzyme leach, can achieve this.

MINERALIZATION MODELS

More regional- and district-scale approaches will provide new exploration guidelines. Basin morphology and sedimentary evolution in relation to submarine volcanic activity will help identify the most favorable areas for sedimentary-exhalative or volcanic-exhalative base-metal deposits.

Similarly, stratabound disseminated Ni, Mo, PGE, and REE deposits, which can occur in more reducing conditions (graphitic beds) near platform carbonates, could be located by correlating magnetic and radiometric anomalies, and geologic data.

Calc-alkaline granite doming in a paleo-subduction environment, identified by indirect depth indicators (gravimetric data) and geochemical pathfinders indicating vertical zoning, could be used to locate new porphyry and epithermal Au-Ag mineralization.

A surface geochemical halo must not simply be interpreted as belonging to one partivular or telescoped system (s), but also with respect to the multistage paleosurface evolution of the Shield. Supergene enrichment, even during the Proterozoic, can have totally changed the economic parameters of, e.g., a low-grade disseminated deposit.

Deep crustal shear zones with remnants of an obducted oceanic floor (e.g., listwaenite) are favorable for fluid circulation and gold deposition.

New styles of PGE mineralization have been described from ophiolites around the world; PGEs, the price of which is still increasing, have never been really systematically explored for in Saudi Arabia and several favorable targets are known in the Shield.

GIS APPLICATIONS

Integrating new databases into the GIS should enhance the selectivity of searches for potentially mineralized areas:

Thematic analysis could use Landsat TM images, with specific processing for delineating alteration halos (like iron rich layers, water, OH-rich aureoles, etc.)

Radiometric multichannel coverage of the Shield is needed

Regional geochemical surveys should include multi-element data and low detection limits for Au and selection of the finest fraction to avoid pollution by wind-blown particles

A regional heavy-mineral survey should provide additional information of value.

TECHNIQUES

At the prospect scale, using PIMA (infra red spectroscopy) to delineate alteration haloes will give better correlation between the lithology and the variations in reg or bedrock geochemistry.

Where a regional anomaly is found, a partial-extraction technique on the corresponding heavy-concentrate samples may provide useful indicators of the primary source before starting costly grid sampling.

ECONOMICS

An updated metallogenic framework encompassing most of the MODS entries will give more weight to certain unexpected criteria, and the new priority ranking of these occurrences should provide a strong incentive for attracting mineral exploration investors.

This is particularly true within this period of increasing world metal consumption in response to optimistic economic forecasts for the next five years. Between 1998 and 2000, the average base-metal price increased by 30%. The strongest demand increase was for Ni and PGE. Aluminum and magnesium (some altered ultramafics in Saudi Arabia are favorable) are increasingly used in new-car manufacturing.

Final conclusion

It should be remembered that most of the major deposits discovered to date in Saudi Arabia are located near ancient workings. However, during regional geochemical prospecting in favorable districts, several mineral occurrences were identified that had no ancient workings to mark their location. Examples are Shayban, Ar Rjum zinc, Ghadarah, and Al Himar. This shows that systematic exploration of Shield areas with thin sand cover, using an integrated multi-method approach, is a viable proposition.:

Future mineral-exploration activities in Saudi Arabia should include the checking of all remaining anomalies of potential interest. A much more important future activity, however, will be the constant reappraisal of available mineral data in the light of new scientific results and other developments. This is the reason why the Deputy Ministry for Mineral Resources has decided to make a considerable investment in the Integrated Geoscience Database, "IGD".

As in many parts of the world, the mass of available data has been growing almost exponentially, and it has become very difficult to handle data in even one domain because of their sheer volume. The IGD not only facilitates such data manipulation, but also enables the plugging-in of almost unlimited new data, as well as the future recombination of such data in ways as yet unimagined.

Future exploration efforts should include:

- systematic regional coverage of soil geochemistry at regional (1:250,000 to 1:100,000) scales, building up a database of background values for minerals in various geologic settings, and possibly discovering new mineralization.

- a low density geochemical exploration on selected areas of sufficient surface with application of the most up to date methods as applied recently successfully by BRGM in morpho-pedological contexts of desert regions similar to the Arabian Shield, in order to obtain a homogeneous and global geochemical cover on areas with high mineral potential but with a very heterogeneous repartition of the information),

- a high-resolution airborne geophysical survey covering the Shield as well as a wide band of Phanerozoic rocks that may hide shallow, blind, deposits in Proterozoic rocks. The survey should acquire new data on magnetism, electromagnetism, radiometry and gravity,

- a high density aerogeophysical prospections (mag., scintillo...) on selected areas, in order to make available modern, reliable and high quality regional geophysical data allowing data processing and combination with other types of data),

- new radar satellite data should be acquired to have complete coverage of the Shield area, including its sedimentary borders.

- much of the older (e.g., pre-1980) mapping of the Shield and its surrounding area will have to be revised in the light of new stratigraphic data and other geologic concepts, which will require extensive field efforts.

- systematic use of GIS processing of available data should precede any exploration project, whether detailed or regional.

 

In conclusion, it is clear that part of the exploration work should include the continued checking of high potential and under explored known anomalies discovered in the frame of the Arabian Shield project. However, a completely novel type of work will have to be continued in parallel, in order to maintain an integrated data base of the Arabian Shield and to use it to prepare new projects for mineral development over the next quarter century.