A preliminary study on the element abundance in the Hulusimpang Formation, Way Kalianda, Pesawaran, Lampung, Indonesia

Hulusimpang Formation.has known as Oligocene-Miocene rocks that consisted of volcanoclastic rock. Its scope was wide, especially in southern Sumatra. This formation is supposed as a prospect host of various hydrothermal mineralization. A preliminary study was carried out to examine the abundance of elements located in Way Kalianda River, Pesawaran, Lampung. This study was conducted by easuring its stratigraphy and analyzing its composition using an X-Ray fluorescence analyzer. The lithologies generally consist of lapilli tuffs, volcanic breccias, interbeded by claystone and sandstone; in addition, it is also frequently found petrified wood and andesitic-lithic fragments. As a result, the significant abundant elements are Fe (35.5%), Si (27.9%), Al (17.4%), K (6.7%), Cl (5.5%), Ti (1.7%), and Ca (1.5%) and also Mn, Ag, P, Mg, Sr, Zr, and Co. It also presents trace elements such as Rb, Zn, Pb, Te, V, Ba, Cr, Sn, Ni, Ga, Nb, Mo, and Eu. These elements are suggested from distal facies of intermediates-magma series Tertiary volcano.

U - Pb zircon age of gabbro and plagiogranite in Hiep Duc, Quang Nam and their geological significances

The gabbro and plagiogranite magmas of the Ngoc Hoi and Dieng Bong complexes are mainly distributed in the northern part of the Kon Tum block. They were previously considered parts of the Tam Ky - Phuoc Son ophiolite complex. In this study, 02 samples of gabbro and plagiogranite were collected from the Hiep Duc area. Petrographic characteristics showed that the rocks were highly foliated and weakly metamorphosed; the schist formed after the crystallization of the rocks. U - Pb zircon age dating from the gabbro rocks as 497.7±1.4 Ma, similar to the plagiogranite age of 498.0±1.3 Ma. The available results in the northern Kon Tum block and Laos indicate the existence of magma series formed during the Late Cambrian period that is probably extended from the northern Kon Tum block to the northeastern part of Laos. The research results on the northern Kon Tum block also confirmed two types of magma in the area: island - arc magma complex and ophiolite type magma complex.

GEOCHEMISTRY AND PETROGENESIS OF SILLS IN LAVASANAT REGION, TEHRAN, IRAN

The study area is located in Lavasanat region in the east of Tehran Province in the Central Alborz zone. The outcrops in this region are mainly associated with Karaj formation and belong to the upper Eocene to Oligocene periods. These outcrops consist of two intrusions: one in the north and the other in the northeast of Lavasanat. These outcrops are scattered over an area of approximately 337km2. In the study region, there are various intrusive igneous rocks, while numerous intrusive igneous rocks are scattered in the form of sills and dikes. These rocks include a range of rocks from diorite gabbro to diorite, monzonite, and syenite. The weathered colors of these rocks are black, brown and gray. The outcrops of these sills are mainly present in the middle-northern part of the quadrangle geological map of the east of Tehran. In different diagrams of the magma series, the study rocks are classified as alkaline, calc-alkaline, and shoshonite, which may indicate magma contamination. An analysis of the variations of the classical elements and trace elements, the spider plots, and interpretations of these plots confirms the relationship of these rocks with the subduction zone and continental arc. To find the tectonic position of the sills in the study area based on the geochemical diagrams, we selected samples from the within-plate (WIP) and arc zones.

GEOCHEMICAL CHARACTERISTICS OF GOLD-BEARING GRANITOIDS AT AYANFURI IN THE KUMASI BASIN, SOUTHWESTERN GHANA: IMPLICATIONS FOR THE OROGENIC RELATED GOLD SYSTEMS

This study investigates auriferous granitoids from the Esuajah and Fobinso pits within the Ayanfuri environment in the Paleoproterozoic Kumasi basin. The aim is to establish the geochemical characteristics of the granitoid gold ores and the possible deposit type which may influence mineral project development. 13 major and 51 trace elements were analyzed using XRF and ICP-MS devices, respectively. The granitoids are mainly classified as granodiorite that crystallized from a calc-alkaline magma series. The Fobinso granodiorite derived from the partial melting of the Birimian metasedimentary rocks, while the Esuajah granitoid derived from igneous rock melts. The granitoid are linked to magma source depleted in mantle material that contains crustal components through subduction processes. Major oxides of the granitoid vary lowly from the average background values derived for basin type granitoid in such terrains. Generally, the granitoid are enriched in Large Ion Lithophile Elements (LILE), while High Field Strength Elements (HFSE) and base metals are within background values when compared to Primitive Mantle (PM) values. Gold mineralisation is associated with Ag, As, Bi, Sb, Te, Pb and S in the peraluminous granitoids. Geochemical characteristics and field observations identify the deposit style as an orogenic related gold deposit type.

Petrogenesis and depositional environment of paleozoic Sedili and Pengerang Volcaniclastics in East Johor Basin, Peninsular Malaysia

Volcaniclastic rocks in East Johor Basin are found in a relatively great abundance comprising Sedili and Pengerang Formations excluding the metamorphics, siliciclastics, and granites. Since the volcaniclastic rocks are found in a different formation, this study aims to find out the characteristics of each rock. Geology, petrography, and geochemical analyses were elaborated to reveal the petrogenesis and depositional environment in the studied area on the basis of fieldwork data and 24 samples collected from outcrops. The Sedili and Pengerang Formations are dominated by acidic rocks of rhyolite, rhyodacite, ignimbrite, and lava classifiied into calc-alkaline magma series which indicates a subduction-related product. Moreover, those acidic rocks are grouped into active continental margin. Eventhough volcanic rocks in Sedili and Pengerang Formations exhibit similar characteristics, they are different in several major contents. Therefore, it is inferred that both Sedili and Pengerang Formations were deposited in different phase. Coincidentally, depositional environment of both formations is also distinct. Sedili Formation were deposited in the subaerial to shallow marine, meanwhile, Pengerang Formation is interpreted to be deposited in deeper depositional setting.

Variation of Slab Component in Ancient and Modern Merapi Products: A Detailed Look into Slab Derived Fluid Fluctuation over the Living Span of One of the Most Active Volcanoes in Sunda Arc

Holocene eruptions of Merapi have produced both medium-K and high-K calc alkaline series which correspond to products older and younger than 1900 years respectively. The change has been attributed to increasing sediment input as the volcano matures. This study presents two Merapi samples which represent Ancient and Modern Merapi. The two samples are analyzed for subduction components including B, Ba, Sr, and Pb using X-ray fluorescence (XRF) spectrometer and prompt gamma ray analysis (PGA). Our finding shows that Ancient Merapi sample from Plawangan Hill lava is close in affinities with younger than 1900 years high-K magma series. On the other hand, Modern Merapi sample from 2006 eruption juvenile is plotted within medium-K magma series which are observed in eruption products older than 1900 years. Ratios of fluid mobile elements to high field strength element (HFSE) (i.e. B/Nb, Ba/Y, Pb/Nb) consistently show that Ancient Merapi sample has higher input of slab derived fluid than Modern Merapi sample. A model using B/Nb and Ba/Nb suggests that Plawangan magma requires 1.5 % of sediment derived fluid, higher than estimated in 2006 eruption magma (1.2 %) and medium-K series magma, and within the range of high-K series magma, to explain its slab component enrichment. This evidence suggests that slab derived component addition to the sub-arc mantle wedge highly fluctuates over short period of evolution of a volcano. One possible explanation is the presence of veined hydrous metasomatized sub-arc mantle as Merapi magma source which allows melting of different mantle area to produce fluctuation of slab components in the course of evolution of Merapi magmas.