The study integrates mineralogical and chemical characteristics of the chromian spinels from northern Iraq using standard petrographic and scanning microscope techniques as well as electron microprobe analyses in order to better understand their provenance, and the implications thereof. Detrital chromian spinels are found as one of the predominant accessory heavy minerals within fluviatile Miocene and Holocene sediments. In addition, such spinels are also present in the Palaeogene-Neogene and Cretaceous alluvial, deltaic and turbiditic sandstones. The results indicate that most of the chromian spinels have interrelated ranges of Cr/(Cr+Al) at rather low contents of Fe and Ti suggesting that the sandstones which host the chromian spinels were derived from a source area dominated by ultramafic rocks. Mineralogical and chemical data suggest that Alpine-type peridotites were the main source rocks for the studied chromian spinels. All available evidence supports the idea that the sandstones originated from the ophiolite-radiolarite belt of the Taurus Range in northeastern Turkey, as well as from recycling of the uplifted Cretaceous strata of northern Iraq.

Modal analysis, bulk-rock geochemistry and phase chemistry of sandstones of the Miocene Fat’ha and Injana formations, northern Iraq, show that the clastics were derived from heterogeneous sources that include basic igneous and metamorphic rocks as well as older sedimentary rocks. The sandstones are generally carbonate-rich lithic arenites. Their geochemistry supports the petrographic results and indicates that they are all Fe-rich, lithic or quartz arkosic sandstones. According to geochemical data, garnets are derived from metamorphic sources, hornblende is of igneous origin, and clinopyroxenes, are produced by basic igneous rocks. Epidote is most probably to be a product of disintegration of metamorphic rocks, essentially, metamorphosed igneous rocks. Rutile geochemistry implies low-grade metamorphic and basic to ultrabasic igneous sources. Chemical composition of chromian spinels indicates that they are derived from Alpine-type peridotite. The ophiolitic-radiolarite belts of Taurus-Zagros as well as the uplifted Cretaceous and Paleocene strata of north and northeastern Iraq are likely to be the major source of clastics to the Fat’ha–Injana basin, a foreland basin formed as a result of the continental Arabian and Turkish/Iranian plates collision.

ABSTRACT. The drifting sand and dune movement pose serious geohazard on urban development and road construction in the Kingdom of Saudi Arabia. This fact initiated several research projects in a number of universities and research institutes in the Kingdom.Two locations of inter mountain dune fields east and southeast of Jeddah were investigated and the dune forms were identified. In addition to the sand sheets, the major dune type is the reversal linear dunes coexisting with few small barchan dunes.Detailed investigations on the linear dunes indicated that the ultimate direction of movement of the dunes is downwind along their crest line. However, during their migration, the dunes wander laterally in both directions but more in one direction than the other depending on the frequency of the prevailing wind and configuration of the surrounding mountains.The sand from the two locations was found to be similar in their grain size parameters. Some variations, however, were observed both along the crest line and across the dune body. Mineralogically, the sand reflects the composition of the surrounding igneous, metamorphic and sedimentary rocks. The results of cone penetration tests were used to reconstruct a possible cross section for the linear dune which is slightly different from the existing hypothetical sections.A reasonable similarity was obtained between the studied dunes and the linear dunes existing in Al Nufud but some differences were found between the sand from these dunes and the other dune forms in Al Jafurah and Ad Dahna sand seas.The sections of the highways crossing these dune fields are either parallel or intersect the dune crest lines at small angle. The dunes, therefore, pose only minor sand drifting hazard on these highways. A forest is suggested to be established to control this hazard and minimize the waste water ponding problems.

Chalki basalts as a small body of volcanic rocks have green to grayish green color due to their nearly complete alteration to chlorite. The essential minerals of Chalki basalt to andesitic basalts are plagioclase (labradorite, An 51-61 ; andesine, An 35 to An 42 ; and oligoclase, An 22). Moreover, there is sodic plagioclase (albite, An 0.1 to An 04) whose coexistence with the other more calcic plagioclase means that albitization had occurred. The other essential mineral is pyroxene (endiopside, en 66-68 wo 27-28 fs 05-06 ; and subcalcic augite, en 72 wo 14 fs 14). Olivine (Fo 80-81) is also present. According to the NiO content (0.11-0.12 wt%) in olivine grains, they are interpreted to be originated tectonically. The prevalent chlorite in all the samples is mainly diabantite and penninite, indicating chloritization after the ferromagnesian olivine and pyroxene. Serpentine (type lizardite and chrysotile) is also recorded as lesser alteration product after the forsteritic olivine. Rare secondary hornblende (type magnesiohornblende) is also found. The spinel group as accessory minerals is defined as magnetite, chromian magnetite, and chromian spinel giving the imprints of their metamorphic origin due to low temperature sub-sea metamorphism and also of alpine type.