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Reconnaissance Geology of the Al Qasr Quadrangle, Sheet 27/41C, Kingdom of Saudi Arabia by I/ I/ Douglas B

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Reconnaissance Geology of the Al Qasr Quadrangle, Sheet 27/41C, Kingdom of Saudi Arabia by I/ I/ Douglas B DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY Reconnaissance geology of the Al Qasr quadrangle, sheet 27/41C, Kingdom of Saudi Arabia by I/ I/ Douglas B. Stoeser and James E. Elliott Open-File Report 85-665* Report prepared for Ministry of Petroleum and Mineral Resources, Deputy Ministry for Mineral Resources, Saudi Arabia This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards and stratigraphic nomenclature J_/ U.S. Geological Survey, Denver, CO 1985 CONTENTS Page ABSTRACT INTRODUCTION........................................ 2 Geographic setting.............................. 2 Previous investigations......................... 2 Present investigations.......................... 4 Acknowledgments................................. 4 GEOLOGIC SETTING PRECAMBRIAN SEDIMENTARY, VOLCANIC, AND METAMORPHIC ROCKS............................................. 7 Banana formation................................ 7 Hadn formation. ..........................'....... 7 PRECAMBRIAN TO CAMBRIAN PLUTONIC ROCKS.............. 16 Metadiabase..................................... 16 Mawgag complex.................................. 16 Tonalite........................................ 16 Pendant tonalite................................ 17 Jadid syenogranite.............................. 17 Foliated granite................................ 17 Jarkuk microgranite............................. 20 Syenogranite.................................... 20 'Ishsh monzogranite............................. 21 Ha 1 il granite....................... .*........... 21 Granodiorite megabreccia........................ 22 Biotite quartz monzonite........................ 22 Undifferentiated granitoid...................... 22 Gabbro.......................................... 22 Granite porphyry................................ 23 Shuqayq microgranite............................ 24 Jufayfah granite................................ 24 Hypabyssal rhyolite............................. 24 Biotite monzogranite............................ 25 Sunaynah granite................................ 25 Biotite syenogranite and quartz syenite......... 25 Biotite alkali-feldspar granite................. * 26 Pethite granite and quartz syenite.............. 26 Biotite-hornblende quartz diorite............... 26 Kifantah alkali-feldspar granite................ 27 Hornblende alkali-feldspar granite.............. 27 Al Rumayh alkali-feldspar granite............... 27 Dikes........................................... 28 Sarrah alkali rhyolite.......................... 28 Muscovite-biotite alkali-feldspar granite....... 29 Alkali apogranite............................... 30 Paqe Aja suite.......................................... 30 Alkali-feldspar granophyre and alkfali granite.... 30 Jabal Aja intrusive complex...................... 31 Arfvedsonite-aegirine alkali granite......... 31 Aegirine alkali granite...................... 31 Porphyritic alkali granite................... 31 Pendant granophyre........................... 32 Pink core granophyre......................... 34 Marma granite................................ 34 Alkali micrographic granite.................. 35 Red granophyre............................... 35 Porphyritic rhyolite. ..*.... ."^............... 35 TERTIARY OLIVINE BASALT................................ 36 QUATERNARY SURFICIAL DEPOSITS .......................... 38 Eolian sand........................................ 38 Alluvium........................................... 38 STRUCTURE AND METAMORPHISM............................. 39 PRECAMBRIAN GEOLOGIC HISTORY AND GEOCHRONOLOGY......... 43 ECONOMIC GEOLOGY....................................... 46 DATA STORAGE........................................... 47 REFERENCES CITED................. % ..................... 48 ILLUSTRATIONS [Plate in pocket] Plate 1. Reconnaissance geologic map of the al Qasr quadrangle Figure 1. Index map showing the location of the al Qasr quadrangle.......................... 3 Figure 2. Generalized geologic map of the al Qasr quadrangle.................................. 6 Figure 3. Silica versus total alkalis binary diagram of al Qasr volcanic rocks........... 10 Figure 4. Partial stratigraphic column of the Hadn formation.............................. 12 Figure 5. Partial stratigraphic column of the Hadn formation.............................. 13 ii Paqe Figure 6. Normative albite-orthoclase-anorthite_ ternary diagram for Hadn rhyolites and granitic rocks.............................. 19 Figure 7. Quartz-alkali feldspar-plagioclase ternary modal diagram for pre-Hadn formation plutonic rocks.................... 19 Figure 8. Quartz-alkali feldspar-plagioclase ternary modal diagram for post-Hadn formation pre-dike swarm plutonic rocks..... 23 Figure 9. Quartz-alkali feldspar-plagioclase ternary modal diagram for Aja suite plutonic rocks.............................. 32 Figure 10. Geologic map of the Ha 1 il region showing late post-orogenic dike swarms and granites................................ 42 TABLES Table 1. Major and trace element analyses for Birkah and Hadn formation volcanic rocks....................................... 8 Table 2. Major and trace element analyses for pre-Aja suite intrusive rocks................ 18 Table 3. Major and trace element analyses for Aja suite rocks............................. 33 Table 4. Major and trace element analyses for Tertiary olivine basalts.................... 37 iii RECONNAISSANCE GEOLOGY OF THE AL QASR QUADRANGLE, SHEET 27/41 C r KINGDOM OF SAUDI ARABIA By !/ i/ Douglas B. Stoeser and James E. Elliott ABSTRACT The Al Qasr quadrangle is located in the northeastern part of the Arabian Shield between lat 27°00 I N. and 27°30' N., and long 41°00' £. and 41°30' E. Except for a fi'eld of Miocene olivine basalt plugs and necks, the quadrangle is underlain by rocks of -the shield. Two Precambrian layered rock units were recognized: the Banana formation (less than 735 Ma) , which is composed of metabasalt and tentatively correlated with the Hulayfah group, and the Hadn formation (about 613 Ma) , correlated with the Shammar group, which consists of rhyolitic ignimbrite flows and cataclastic deposits intercalated with arkosic clastic sediments and minor basalt to andesite flows and sills. Plutonic rocks dominate the quadrangle and form four main groupings. The oldest grouping is composed chiefly of diorite, quartz diorite, tonalite and granodiorite and is probably associated with the Banana formation. The second grouping consists of cataclastically deformed, foliated, and lineated monzogranites and syenogranites, and represents an episode of regional deformation in the Ha'il region. The most extensive grouping of intrusive rocks are weakly deformed to undeformed biotite + hornblende granites and granodiorites that form small to major batholiths. The Hadn formation volcanic rocks are the extrusive equivalent of these rocks. The final phase of plutonism was the emplacement of widespread alkali-feldspar and alkali granites, and alkali rhyolite dikes. The Banana formation and the early dioritic to tonalitic rocks are interpreted to be related to an island arc. The cataclastically deformed and foliated granitic rocks may be related to a major episode of continental collision in the Arabian Shield when the Arabian neocraton formed. Subsequent to initial collision, voluminous intracratonic granites were generated. The intracratonic plutonism culminated in the emplacement of the alkali granitic rocks, when the Ha'il region underwent regional extension, and major east-striking alkali dike swarms formed. JL/ U.S. Geological Survey, Denver, CO No ancient mines or significant mineral occurrences are known within the quadrangle. The only reported mineral occurrences are three fluorite-bearing veins in the Jabal Aja intrusive complex, one of which contains wolframite. Although the mineral potential appears minimal, the possible existence of one or more caldera structures, and the occurrence of an alkali apogranite intrusion and a zinnwaldite(?)-bear ing, peraluminous alkali-feldspar granite, indicate a potential for Sn, W, Ta, Nb, Th, REE, Mo, and Au mineralization. INTRODUCTION Geographic setting The al Qasr quadrangle occupies a 2,7-50 km2 region of the northeastern part of the Arabian Shield (fig. 1), southwest of the city of Ha'ii. Physiographicaliy, the quadrangle is divided by a highlands axis which runs from Jabal Hadn in the southwest to the granite mountains of Jabal Aja in the northeast (see plate) . To the east and west of this axis the quadrangle is typically flat pediment with scattered hills and inselbergs. The highlands axis is sufficiently rugged that only a few roads in the central part of the quadrangle allow access between the western and eastern parts (plate). The pediment surface lies at altitudes of about 1100-1200 meters above sea level (a.s.l.), with a maximum elevation on Jabal Hadn of about 1400 meters a.s.l., and on Jabal Aja of about 1500 meters a.s.l. The quadrangle contains a number of older farming villages such as al Qasr, Mawqaq, and Shuqayq, and new agricultural developments that are expanding rapidly (plate). The al Qasr quadrangle is named for the farming village of Al Qasr that is located in the northeastern quarter of the quadrangle. The name translates literally to the castle or fort, and refers to an old adobe fort in the village. Previous investigations The earliest geologic mapping that includes the al Qasr quadrangle is the 1:500,000-scale geologic map of the North­ eastern Hijaz
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