A corundum-quartz assemblage in altered volcanic rocks, Bond Range, Tasmania

1998 ◽  
Vol 62 (3) ◽  
pp. 325-332 ◽  
Author(s):  
R. S. Bottrill
Keyword(s):  
Volcanic Rocks ◽  
Low Pressure ◽  
Moderate Temperature ◽  
Quartz Porphyry ◽  
Mutual Contact ◽  
Rare Phenomenon ◽  
Argillic Alteration ◽  
Placer Deposits ◽  
Advanced Argillic Alteration

AbstractUnusual corundum-bearing rocks occur in the Bond Range, northern Tasmania, in a hydrothermally altered Cambrian quartz porphyry. The assemblage exhibits quartz and corundum in mutual contact, a rare phenomenon, in association with andalusite, pyrophyllite, diaspore and other minerals. This metastable assemblage apparently resulted from advanced argillic alteration at moderate temperature and low pressure, followed by rapid depressurisation accompanying boiling of hydrothermal, granite-derived fluids. This corundum occurrence appears to be unrelated to the sapphires in placer deposits in Tasmania.

scholarly journals NEW FIND OF ZUNYITE IN ADVANCED ARGILLIC ALTERATION OF RHYOLITES, KOS ISLAND, SOUTH AEGEAN VOLCANIC ARC , GREECE

2004 ◽  
Vol 36 (1) ◽  
pp. 474 ◽  
Author(s):  
D. Papoulis ◽  
P. Tsolis-Katagas ◽  
C. Katagas
Keyword(s):  
Raman Spectroscopy ◽  
Hydrothermal Alteration ◽  
Volcanic Rocks ◽  
Hydrothermal Fluids ◽  
Accessory Mineral ◽  
Volcanic Arc ◽  
Argillic Alteration ◽  
Edx Analyses ◽  
Advanced Argillic Alteration

Zunyite [Ali3SÌ5C>2o(OH,F)i8CI], an extremely rare mineral, was found as an accessory mineral in highly altered rhyolitic rocks at Kefalos, southwestern Kos, and in a completely kaolinized rhyolitic dyke at Asfendiou, northeastern Kos. It is associated with dickite, kaolinite, quartz and minor pyrophyllite. Kos Island contains both Tertiary and Quaternary volcanic rocks. Zunyite has been identified by XRD and studied by SEM, EDS, Raman spectroscopy and FTIR spectroscopy. The presence of zunyite, in the highly altered samples is significant for the determination of the conditions of the hydrothermal alteration that took place. Zunyite crystals, are up to 90 pm in diameter but usually are less than 10 pm; the crystals are partly covered by kaolinite layers. EDX analyses on the surface of zunyite revealed AI2O3/S1O2 values raging from 2.6 to 2.7. The occurrence of zunyite suggests incorporation of hydrothermal fluids rich in F" and CI", thus indicating contamination by seawater

Chapter 22: Gold Deposits of the Yanacocha District, Cajamarca, Peru

2020 ◽  
pp. 451-465
Author(s):  
Richard Pilco ◽  
Sean McCann
Keyword(s):  
Joint Venture ◽  
Volcanic Rocks ◽  
Gold Deposits ◽  
Epithermal Gold ◽  
Sulfide Deposits ◽  
High Sulfidation ◽  
Significant Potential ◽  
Argillic Alteration ◽  
Northern Peru ◽  
Advanced Argillic Alteration

Abstract The Yanacocha district of northern Peru has produced >37 million ounces (Moz) Au since production commenced in 1993. Recognized as one of the world’s most prolific high-sulfidation epithermal gold districts, its discovery was made over a four-year period (1984–1988) through a joint venture alliance operated by Newmont Corporation. Over the past 30 years the geologic understanding of the district has been enhanced by research and documentation by many academic and Newmont geoscientists. The gold deposits are hosted within Tertiary volcanic rocks consisting of pyroclastic sequences cut by several generations of breccias and intrusions, all of which have undergone silicic and advanced argillic alteration. A dominant NE-trending structural corridor bounds all deposits in the district, and local northwest fault intersections with this trend are complimentary controls on mineralization. There are 12 major deposits discovered and exploited at Yanacocha. The largest, Cerro Yanacocha, has produced >17.5 Moz Au, whereas the newest deposit to be delineated, Antonio, has a >1.0 Moz resource. The depletion of shallow, supergene-oxidized deposits has necessitated the current underground development to exploit deeper sulfide deposits. Significant potential remains within the Yanacocha district in both oxide and sulfide deposits, and ongoing exploration efforts, are leveraging learnings from mined deposits and advances in exploration technologies and tools to extend the mine life.

Chapter 23: Alteration, Mineralization, and Age Relationships at the Kışladağ Porphyry Gold Deposit, Turkey

2020 ◽  
pp. 467-495
Author(s):  
T. Baker ◽  
S. Mckinley ◽  
S. Juras ◽  
Y. Oztas ◽  
J. Hunt ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
White Mica ◽  
Western Anatolia ◽  
Low Grade ◽  
Porphyry Deposits ◽  
Magmatic Arc ◽  
Argillic Alteration ◽  
Metamorphic Basement ◽  
Slab Tear ◽  
Roll Back

Abstract The Miocene Kışladağ deposit (~17 Moz), located in western Anatolia, Turkey, is one of the few global examples of Au-only porphyry deposits. It occurs within the West Tethyan magmatic belt that can be divided into Cretaceous, Cu-dominant, subduction-related magmatic arc systems and the more widespread Au-rich Cenozoic magmatic belts. In western Anatolia, Miocene magmatism was postcollisional and was focused in extension-related volcanosedimentary basins that formed in response to slab roll back and a major north-south slab tear. Kışladağ formed within multiple monzonite porphyry stocks and dikes at the contact between Menderes massif metamorphic basement and volcanic rocks of the Beydağı stratovolcano in the Uşak-Güre basin. The mineralized magmatic-hydrothermal system formed rapidly (<400 kyr) between ~14.75 and 14.36 Ma in a shallow (<1 km) volcanic environment. Volcanism continued to at least 14.26 ± 0.09 Ma based on new age data from a latite lava flow at nearby Emiril Tepe. Intrusions 1 and 2 were the earliest (14.73 ± 0.05 and 14.76 ± 0.01 Ma, respectively) and best mineralized phases (average median grades of 0.64 and 0.51 g/t Au, respectively), whereas younger intrusions host progressively less Au (Intrusion 2A: 14.60 ± 0.06 Ma and 0.41 g/t Au; Intrusion 2 NW: 14.45 ± 0.08 Ma and 0.41 g/t Au; Intrusion 3: 14.39 ± 0.06 and 14.36 ± 0.13 Ma and 0.19 g/t Au). A new molybdenite age of 14.60 ± 0.07 Ma is within uncertainty of the previously published molybdenite age (14.49 ± 0.06 Ma), and supports field observations that the bulk of the mineralization formed prior to the emplacement of Intrusion 3. Intrusions 1 and 2 are altered to potassic (biotite-K-feldspar-quartz ± magnetite) and younger but deeper sodic-calcic (feldspar-amphibole-magnetite ± quartz ± carbonate) assemblages, both typically pervasive with disseminated to veinlet-hosted pyrite ± chalcopyrite ± molybdenite and localized quartz-feldspar stockwork veinlets and sodic-calcic breccias. Tourmaline-white mica-quartz-pyrite alteration surrounds the potassic core both within the intrusions and outboard in the volcanic rocks. Tourmaline was most strongly developed on the inner margins of the tourmaline-white mica zone, particularly along the Intrusion 1 volcanic contact where it formed breccias and veins, including Maricunga-style veinlets. Field relationships show that the early magmatic-hydrothermal events were cut by Intrusion 2A, which was then overprinted by Au-bearing argillic (kaolinite-pyrite ± quartz) alteration, followed by Intrusion 3 and late-stage, low-grade to barren argillic and advanced argillic alteration (quartz-pyrite ± alunite ± dickite ± pyrophyllite). Gold deportment changes with each successive hydrothermal event. The early potassic and sodic-calcic alteration controls much of the original Au distribution, with the Au dominantly deposited with feldspar and lesser quartz and pyrite. Tourmaline-white mica and argillic alteration events overprinted and altered the early Au-bearing feldspathic alteration and introduced additional Au that was dominantly associated with pyrite. Analogous Au-only deposits such as Maricunga, Chile, La Colosa, Colombia, and Biely Vrch, Slovakia, are characterized by similar alteration styles and Au deportment. The deportment of Au in these Au-only porphyry deposits differs markedly from that in Au-rich porphyry Cu deposits where Au is typically associated with Cu sulfides.

Age and origin of advanced argillic alteration at the Bor Cu-Au deposit, Serbia

2005 ◽  
pp. 541-544
Author(s):  
C. Lerouge ◽  
L. Bailly ◽  
E. Béchu ◽  
C. Fléhoc ◽  
A. Genna ◽  
...  
Keyword(s):  
Argillic Alteration ◽  
Advanced Argillic Alteration

Synchronous advanced argillic alteration and deformation in a shear zone-hosted magmatic hydrothermal Au-Ag deposit at the Temora (Gidginburg) Mine, New South Wales, Australia

1995 ◽  
Vol 90 (6) ◽  
pp. 1570-1603 ◽  
Author(s):  
Andrew H. Allibone ◽  
Geoffrey R. Cordery ◽  
Gregg W. Morrison ◽  
Subhash Jaireth ◽  
Jeffrey W. Lindhorst
Keyword(s):  
Shear Zone ◽  
New South ◽  
New South Wales ◽  
South Wales ◽  
Argillic Alteration ◽  
Advanced Argillic Alteration

Petrology and geochemistry of the Kamloops Group volcanics, British Columbia

1981 ◽  
Vol 18 (9) ◽  
pp. 1478-1491 ◽  
Author(s):  
Thomas E. Ewing
Keyword(s):  
British Columbia ◽  
Fractional Crystallization ◽  
Middle Eocene ◽  
Volcanic Rocks ◽  
Primary Source ◽  
Low Pressure ◽  
Rock Types ◽  
South Central ◽  
High K ◽  
Petrology And Geochemistry

The Kamloops Group is an alkali-rich calc-alkaline volcanic suite of Early to Middle Eocene age, widespread in south-central British Columbia. Rock types in the suite range from high-K basalt through andesite to rhyolite. The suite is characterized by relatively high K2O, Sr, and Ba, but low Zr, Ti, and Ni concentrations, only moderate Ce enrichment, and little or no Fe enrichment. Initial ratios 87Sr/86Sr are about 0.7040 in the western half, and about 0.7060 in the eastern half of the study area. No difference in chemistry or mineralogy marks this sharp transition. Chemically similar suites include the Absaroka–Gallatin suite in Wyoming and the lower San Juan (Summer Coon) suite in Colorado. The content of K2O at 60% SiO2 increases regularly eastward across southern British Columbia. The chemical data support the subduction-related continental arc origin of the Kamloops Group volcanics.The volcanic rocks consist in the main of augite–pigeonite andesites ranging from 52 to 62% silica, with subordinate quantities of olivine–augite–pigeonite basalt and biotite rhyodacite and rhyolite. The andesites and basalts were derived by a combination of low-pressure fractional crystallization, higher pressure fractional crystallization, and variable parental magmas, whereas low-pressure fractional crystallization of plagioclase, biotite, and apatite from parental basalt and andesite produced the rhyolites. The parental magmas were basalts and basaltic andesites with high K, Sr, and Ba. The primary source of these magmas is inferred to have been an alkali-enriched hydrous peridotite with neither plagioclase nor garnet present in the residuum.

scholarly journals KAITAN TIPOLOGI PANTAI DENGAN KEBERADAAN PASIR BESI DI PANTAI MUKOMUKO, BENGKULU

2016 ◽  
Vol 10 (2) ◽  
pp. 59
Author(s):  
Udaya Kamiludin ◽  
Yudi Darlan ◽  
Deny Setiady
Keyword(s):  
Volcanic Rocks ◽  
Relative Magnitude ◽  
Source Rocks ◽  
Frequency Content ◽  
Sand Beach ◽  
Basaltic Rocks ◽  
Basaltic Composition ◽  
Waves And Currents ◽  
Placer Deposits ◽  
Gravel Beach

Pasir besi merupakan salah satu potensi di sebagian kawasan pantai Indonesia yang erat kaitannya dengan keberadaan kondisi geologi batuan bersusunan andesitik-basaltik, oleh sebab itu salah satunya dipilih pantai Mukomuko sebagai objek penyelidikan. Pasir besi ini terakumulasi sebagai endapan alokhton dari hasil pelapukan dan erosi tanah yang diangkut oleh sungai dan diendapkan di pantai. Proses marin berupa abrasi dan akrasi terbentuk di sepanjang garis pantai oleh pemusatan gelombang dan arus sejajar pantai. Metode penyelidikan meliputi deskripsi kualitatif karakteristik pantai, penentuan posisi, pemercontohan sedimen, analisis megaskopis, dan pemisahan mineral bersifat magnetik dengan menggunakan magnet tangan disertai foto mikrograf. Tipologi pantai Mukomuko terdiri dari gisik berpasir (Sand beach) yang sebagian di atasnya ada bangunan dinding laut, dan gisik berkerikil (Gravel beach). Endapan pasir besi umumnya menempati gisik berpasir, baik pada muka pantai maupun pada tanggul gisiknya yang sebagian membentuk pematang pantai. Distribusi persentase magnetit (% Fe) sejajar pantai memiliki pola besaran relatif sama dengan kadar frekuensi yang berkisar antara 0 % - 10 %, anomali dijumpai secara setempat pada tanggul gisik dengan kisaran antara 30,07 % - 45,73 %. Berdasarkan klasifikasi cebakan plaser, genesa pasir besi terkonsentrasi oleh media cair yang bergerak sebagai jenis plaser pantai yang dipengaruhi oleh fluviatil. Keterdapatan pasir besi diduga berasal dari Formasi Hulusimpang yang dikorelasikan sebagai Andesit Tua, Batuan Gunungapi Kuarter dan lapisan konglomerat aneka bahan Formasi Bintunan yang bersusunan andesitik-basaltik. Kata Kunci : Karakteristik pantai, magnetit, plaser pantai, sumber batuan, pantai Mukomuko Bengkulu. Iron sand is one of the mineral potential in some coastal areas of Indonesia, which is related to the presence of andesitic-basaltic rocks, therefore Mukomuko coast is then selected as the object of investigation. The iron sand is accumulated as the alochton deposit as the product of the weathering and soil erosion transported by the river and it is accumulated on the beach. The abrasion and accretion processes are formed along the shoreline by waves and currents parallel to the coast. The methods of investigation include coastal characteristics mapping, positioning, sediment sampling, megascopic analysis, and magnetic separation of minerals by using a hand magnet with micrograph photo. The coastal characteristics of Mukomuko consist of gravel beach, and sand beach that some sea walls built on. Iron sand deposits generally occupy a sand beach, either on the beach face or on the berm which partially form the beach ridge. The distribution of magnetite parallel to the coast has the same relative magnitude patterns with the frequency content ranging from 0 % - 10 %, anomaly is found locally on the berm with the frequency content ranging between 30.07 % - 45, 73 %. Based on the classification of placer deposits, iron sand is concentrated in the formation of moving liquid media as placer beach types affected fluvial. The presence of iron sand supposed to be derived from the Hulusimpang Formation is correlated as Old Andesite, Quaternary Volcanic Rocks and conglomerate layers of different materials of andesitic-basaltic composition from Bintunan Formation. Keywords: Coastal Characteristics, magnetite, beach placer, source rocks; shore of Mukomuko, Bengkulu.

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