PROVENANCE AND TECTONIC SETTING OF SOME PALEOPROTEROZOIC SEDIMENTARY ROCKS IN THE CHAGUPANA AND TARKWA AREAS OF GHANA: PETROGRAPHIC AND STRUCTURAL CONSTRAINTS

Paleoproterozoic sedimentary rocks associated with the Man Shield of West Africa are perceived to be similar, irrespective of their locality. This research seeks to establish the provenance and tectonic setting of these rocks to ascertain any such similarity perception, based on information from two localities. The study uses modal mineral estimations to reconstruct the source, paleocurrent, paleoclimate and relief of some conglomerates and sandstones from Chagupana and Tarkwa areas in Ghana. Chagupana conglomerate has igneous and metamorphic provenances, while Kawere conglomerate has metamorphic provenance. Average mineralogical composition of Chagupana sandstone is Q53-F45-R3 and classify as arkose. Tarkwa suites of Huni, Kawere and Banket sandstones are composed of Q48-F34-R18, Q51-F25-R23 and Q76-F7-R17, and classify as lithic arkose, lithic arkose-feldspathic litharenite, and sublitharenite, respectively. Detritus of all the sandstones suggest acid igneous rock source, with minor sedimentary and metamorphic imprints, with an order of maturity as Banket>Kawere>Huni>Chagupana. Detritus in the Chagupana, Huni and Kawere sandstones are from the transitional continental margin. The Chagupana is from the cold arid climate, while the Huni and Kawere are from the semi-arid/semi-humid climates. The Banket sandstone mobilises from craton interior with recycled orogenic materials in a humid environment. The angular-subangular feldspars in Chagupana sandstone indicate low relief and low-moderate recycling close to the source. Huni, Kawere and Banket sandstones derive from low-moderate reliefs with multiple recycling episodes. The Chagupana and Huni sandstones show paleo-current directions from the north and east, respectively. Similarities between the Chagupana and Tarkwa rocks can only be limited to the tectonic setting and not from source area, paleo-climate, paleo-current and relief.

Chapter 37: Giant Placers of the Upper Kolyma Gold Fields, Yana-Kolyma Province, Russian Northeast

The Upper Kolyma gold placers of northeastern Russia produced 2,700 metric tons (t) Au. Approximately 40% of this gold was extracted from just five placers, Chai-Yuria, Berelekh, Maldyak, Malyi At-Yuryakh, and Omchak, and their immediate tributaries. The placers were derived from Late Jurassic to Early Cretaceous lode deposits, formed during sinistral translation subsequent to the Kolyma-Omolon superterrane accretion to the Verkhoyansk passive margin of the Siberian craton. The metallogenic events produced either abundant and widespread small quartz veins or more localized large to superlarge quartz stockworks and disseminated gold deposits. These orogenic gold deposits acted as a principal hard-rock source during formation of the gold placers, beginning in the Late Cretaceous but most importantly during the Cenozoic. Tectonic, geomorphologic, and climatic factors at a triple junction of the North American, Eurasian, and Okhotsk lithospheric plates provided the ultimate controls on placer formation.

INDIKASI LEMBAH PURBA SEBAGAI WADAH MINERAL PLASER DAN UNSUR TANAH JARANG DI PERAIRAN TANJUNG BERIKAT DAN SEKITARNYA, BANGKA TENGAH, BANGKA BELITUNG

Secara regional daerah Bangka merupakan bagian dari Jalur Granit Utama Pembawa Timah. Daratan nya ditandai oleh intrusi Granit Klabat yang merupakan batuan penting sumber endapan plaser. Untuk mengetahui lembah purba maka dilakukan perekaman seismik saluran tunggal. Daerah penelitian secara administratif merupakan bagian dari wilayah Kabupaten Bangka Tengah, Propinsi Bangka Belitung. Perairan Tanjung Berikat dan sekitarnya dicirikan oleh kelerengan dasar laut rata-curam dengan kedalaman terukur antara 0-45 meter. Interpretasi seismik saluran tunggal menunjukkan stratigrafi seismik dari muda ke tua yaitu Runtunan A, Runtunan B, intrusi, dan Runtunan C sebagai dasar akustik. Ketebalan sedimen Runtunan A antara 5-30 meter dari permukaan dasar laut. Lembah purba memanjang cukup lebar dan dalam pada Runtunan B yang diduga sebagai fasies pengisian lembah berupa onlap fill. Fasies ini memiliki internal reflektor bebas pantulan-kaotik yang ditafsirkan sebagai wadah mineral plaser dan mineral ikutan pembawa unsur tanah jarang. Endapan plaser diperkirakan merupakan hasil pengerjaan ulang batuan granitoid.Kata Kunci : Dasar laut, runtunan stratigrafi, lembah/alur Purba, endapan plaser, dan Perairan Tanjung Berikat dan Sekitarnya, Bangka-Belitung. Geologically regional, the Bangka area is part of the Main Tin Belt Granite. The mainland of the study area is characterized by Klabat Granite intrusion which is an important rock source of placer deposits. To find out the placer availability of deposits on Paleo channel it was carried out for the recording of single channel seismic data. The study area is administratively part of the area of Central Bangka, Bangka-Belitung Province. Tanjung Berikat waters and its vicinity are characterized by the slope of the flat sea floor to steep with a measured depth of 0-45 meters. Seismic interpretation shows seismic stratigraphic from young to old consisting of sequence A, sequence B, Intrusion, and sequence C as acoustic basement. Sediment thickness of sequence A between 5-30 meters from seafloor surface sediment. Paleo channel with an elongated shape that is wide enough and deep in sequence B is interpreted as a channel filling facies in the form of onlap fill. This facies is characterized by the free to chaotic reflector configuration which is interpreted as a place for mineral placer and accessory minerals which contain rare earth elements. The availability of placer deposits is interpreted as the result of reworking of granitoid source rock.Keywords: Sea floor, stratigraphic seismic, Paleo channel, placer deposits, and Tanjung Berikat waters and surrounding, Bangka-Belitung.

Petrographic Analysis of Basalt Artifacts from Three Aleutian Sites

By comparing thin sections of basalt artifacts from three early and middle Holocene Aleutian sites with geological samples, we can infer the location of the artifactual rock source or sources. Contrary to the sources, the comparison shows that the basalt artifacts came from a single flow or closely related flows 15-30 km from all three sites. This finding suggests we should reassess the role of cultural continuity, trade, and exchange in the early and middle Holocene of the Aleutians.