Domestic demand for feldspar is growing in the Kingdom, mainly for use in ceramic and glass industries, and the expected increase in the near future because of the rapid industrial development. Silspar a purified mixture of about 45-50% free silica (quartz) and 50-55% feldspar is produced through upgrading weathered leucocratic granite and feldspathic sand. The disappointing results of feldspar and nepheline syenite reconnaissance (Barasheed and others, 1994) demonstrated small feldspar and nepheline syenite resources in the Kingdom. The present study is based on investigations in the governorates of Ar Riyad, Al Madinah al Munawwarah, and Makkah al Mukarramah areas probing for feldspathic sand in wadi beds and for weathered intrusive leucocratic granite plutons suitable for silspar-upgrading.
• In the Ar Riyad governorate area, a portion located some 160 km west-southwest of Ar Riyad, 71 occurrences were visited and sampled, 53 samples were selected for chemical analysis, and 8 for petrographic study. Based on the field survey and laboratory results, the potentially most favorable geologic rock unit that contains widespread weathered granite and feldspathic-sand deposits is rock unit Mg1 of the Murdama group. The samples collected from this unit revealed homogeneous alkali-feldspar granite with the following average contents SiO2 75.50%, Fe2O3 1.30%, Na2O 2.93% and K2O 4.50%, 39 out of 53 samples show favorable characteristics for silspar or feldspar upgrading tests.
• In the Al Madinah al Munawwarah governorate area, 55 occurrences were visited and sampled; 19 samples from Madinah and 15 from Yanbu were selected for chemical analysis, and 8 samples for petrographic study. Here, too, the Mg rock unit is the most favorable one, it is related to the post-Furayh-group in the Al Madinah area, and Hg-alkaline granite which is related to the post-Hadiyah intrusives near Yanbu. Average composition is SiO2 70.80%, Fe2O3 2.47%, Na2O 3.70%, and K2O 3.70% for the Madinah area; SiO2 74.78%, Fe2O3 1.34%, Na2O 3.7%, K2O 4.7% for Yanbu area. The test results show 23 out of 37 samples (13 samples from Al Madinah and 10 from Yanbu) to have acceptable limits for feldspar and silspar upgrading.
• In the Makkah al Mukarramah governorate area, a brief survey was made of the intrusive Hashafat, Numan, and Shiwan complexes around Makkah and Jiddah, and northeast of Al Lith. The average chemical composition of 6 samples collected from different units showed total SiO2 72.19%, Fe2O3 2.12%, Na2O 3.86%, and K2O 4.03%. Tests showed that 5 out of 6 samples have an acceptable composition for feldspar and silspar upgrading.
• Preliminary results of the upgrading tests have shown the following samples to have good potential for producing silspar and feldspar ceramics, and glass for industries:
• Ar Riyad governorate area
RFS 11A, 53C, 56C, 67, 69A, 70C
• Al Madinah area
MFS 19A, 6A, 6C, 9A, 38, 17A, 3B, 19C, 3A, 18B
• Yanbu area
YFS 9A, 12A, 12B, 16C, 6C, 11C
• Makkah al Mukarramah governorate area
JFS 10A, 15A, 6A
In addition to the samples above, many other samples are being investigated and their results are awaited, particularly from the Ar Riyad governorate area. Various bleaching agents were used during the tests, but hydrochloric acid (10%) and sodium-thiosulfide (10%) were found most suitable and economic for this purpose. Study on the production cost of silspar is not yet completed, but a rough estimate is about 50-55 SR per ton. Detailed investigations are required, including market conditions (to define if silspar as a substitute of feldspar meet the Saudi ceramic and glass factory specifications), trenches, drilling, mapping, chemical and industrial scale upgrading tests, so as to delineate reserves and homogeneity of the deposits, thus confirming or invalidating the proposed targets for exploitation.
Al Nakhebi, Z., Al Ghamdi, S.A., Al Marzouki, H., Habib, M.K., with the collaboration of Siddiqui, A.A., and Al Turky, H., 2001, Investigation of feldspathic sand and wethered leucocratic granite deposits suitable for feldspar and silspar production in the governorates of Ar Riyad, Al Madinah al Munawwarah, and Makkah al Mukarramah, Kingdom of Saudi Arabia: Saudi Geological Survey Open-File Report SGS-OF-2001-6, 39 p., 13 figs, 17 tables, 2 plates