RA-06 : Hydrothermal Breccia TextureHYDROTHERMAL BRECCIA TEXTURE RO CKS A NAYSLIS 2016/3/31 Analisis Batuan @ Rosana 2016 1 Piroklastika jatuhan Proses sedimentasi Kubah lava Leher gunungapi sill Aliran lava retas Volkanisme Kantong magma Dapur magma 2016/3/31 Analisis Batuan @ Rosana 2016 Proses magmatisme 2 STRATIGRAFI/ FASIES VOLCANIC (Bogie & Mackenzie, 1998) 2016/3/31 Analisis Batuan @ Rosana 2016 3 VOLCANIC BRECCIA VOLCANIC BRECCIA is pyroclastic (fire-formed fragments) and forms in explosive eruptions. It is a mix of large angular fragments and small ash. Often, the material is hot when it comes to rest and cools (welds) into a very hard rock. 2016/3/31 Analisis Batuan @ Rosana 2016 4 BRECCIAS Breccia is rocks that composed of clast (fragments) > 2 mm size and angular nor sub-angular shape, cement (hydrotermal mineral or crystalline igneous rock) and open space Grain-size of subdivision of clast are : 2-4 mm fine-grained 4-64 mm medium-grained 64-256 mm coarse-grained > 256 mm very coarse grained Bryner (1968) recognized problem when he ppointed out that many clasts in hydrothermal breccia are mostly rounded, so the term of “breccia” was misleading in these cases Breccias in some cases consists of fragments that are neither angular nor sub-angular (e.g. Pebble breccia) 2016/3/31 Analisis Batuan @ Rosana 2016 5 GENETIC CLASSIFICATION OF BRECCIAS There are seven principal types of breccia comprising 13 sub-types occuring in epithermal-porphyry mineral deposits : I. Instrusive Breccias II. Volcanic Breccias III. Phreatomagmatic Breccias IV. Magmatic-Phreatic Breccias V. Phreatic Breccias VI. Tectonic Breccias VII. Sedimentary Breccias 2016/3/31 Analisis Batuan @ Rosana 2016 6 1. INTRUSIVE BRECCIAS These are subdivided into three members : 1a. Magmatic-Intrusive-Breccias : – Created during the emplacement of an intrusive body – Consist of clasts comprising xenolith of country rocks, including previous intrusives, and fragment of earlycrystallized portionw of the intrusive disrupted during emplacement, in matrix of crystalline igneous material – Frequently occur on the margins of intrusive bodies and contain clast of country rock in a crystalline igneous matrix 2016/3/31 Analisis Batuan @ Rosana 2016 7 1. INTRUSIVE BRECCIAS These are subdivided into three members : 1a. Magmatic-Intrusive-Breccias : – High temperature of emplacement and show reaction rims around the xenoliths – Mineralization in this type of breccias is direct magmatic origin and some reaction with host rocks as in skarn deposit – Important setting for base metal mineralization – In term of exploration: the ore-hosting breccia could be expected to be closely spatially related to the margins of an intrusive, and these area should be explored. 2016/3/31 Analisis Batuan @ Rosana 2016 8 1. INTRUSIVE BRECCIAS These are subdivided into three members : 1b. Magmatic-Hydrothermal Breccias 1c. Magmatic-Tectonic Breccias 2016/3/31 Analisis Batuan @ Rosana 2016 9 2. VOLCANIC BRECCIAS The essentil feature of these breccias is that the energy causing brecciation (and/or) ejection from the volcano) is dependent on the release of pressure of magmatic volatiles. Divided into two sub-types: a) Endogenous Volcanic Breccias (non-eruptive or vent breccias) b) Exogenous (Eruptive) Volcanic Breccias 2016/3/31 Analisis Batuan @ Rosana 2016 10 3. PHREATOMAGMATIC BRECCIAS These are equivalent to hydromagmatic breccias (Sillitoe, 1985). Phreatomagmatism occurs when upwelling magma encounter water. This may be groundwater, connate water, or a body of surface water.Thi breccias divided into : a. Endogenous (non eruptive) phreatomagmatic breccias b. Exogenous Breccias 2016/3/31 (eruptive) Analisis Batuan @ Rosana 2016 Phreatomagmatic 11 4. MAGMATIC-PHREATIC BRECCIAS Occurs through the flashing or expansion of a fluid which is composed of water or steam May contain a proportion of magmatic volatiles but predominantly of meteoric, groundwater or connate origin, and directly heated by the intrusion of magma Does not contain juvenile magmatic products Divided into : A. Edogenous (non-eruptive) Magmatic-Phreatic Breccias B. Exogenous (eruptive) Magmatic-Phreatic Breccias 2016/3/31 Analisis Batuan @ Rosana 2016 12 5. PHREATIC BRECCIAS A phreatic eruption is caused by expansion of steam and gas from a water-dominated fluid, with only a minor component of magmatic volatiles The mechanism of energy transport to the focus of eruption has to be at some point by a freely-conveting column of sub-critical hydrous fluid Reffered as hydrothermal eruption or vent breccia divided into : A. Endogenous Phreatic Breccias B Exogenous Phreatic Breccias 2016/3/31 Analisis Batuan @ Rosana 2016 13 6. TECTONIC BRECCIAS Formed by the mechanical disruption of rocks in response to tectonic stress. May grind clasts to rock flour forming gouge or mylonite Tend to occur in identifiable, usually steeply dipping, fault planes Tectonic breccias are major importance for mineralization in metamorphic terraines If mineralization is associated with a tectonic breccia in nonmetamorphosed volcanic terrain, it is unlikely that the tectonism caused the mineralization, and so the function of the breccia is probably just to provide permeable path for mineralzing fluids. Exploration strategy should consist of tracking the extent of the brecia, and separately interpreting the mineralizing process If mineralization appears to have pre-dated faulting, the possibility of concealed cut-off mineralized zone should be considered. 2016/3/31 Analisis Batuan @ Rosana 2016 14 7. SEDIMENTARY BRECCIAS in the typical epithermal/porphyry environment, they consist principally of volcanic material volcaniclastic sediment range from epiclastic deposits such as laharic or avalanche deposit, that have little evidence of sedimentary processes, through to well-sorted volcanogenic sandstones or pumicities the essential feature of these breccias is that they have been emplaced on the earth’s surface by predominantly sedimentary processes. Features indicative of water transport may be apparent, suh as cross bedding.There may be interbedded non volcanogenic sediments mineralization in this setting is not directly related to brecciation processes In term of exploration, can be apply similar to an exogenous volcanic breccia. The extent and location of the breccia can be predicted by stratigraphy, but the mineralizing processes should be seperately evaluated 2016/3/31 Analisis Batuan @ Rosana 2016 15 DESCRIBING BRECCIAS breccia are very important host rocks for mineralization, not only becouse, of the large surface area they make available for water-rock interaction and the fact that they represent zones of high permeability, but some of the processes of breciation such as hydraulic fracturing can closely related to the process of mineralization He classification is based on the proportions of vein clast, rock clasts, chemically deposited cement, and clastic/igneous matrix within the breccia. When describing breccias,the following features chould be noted : 1. Clast lithologies 2. The shape of clasts 3. The size and size distribution (degree of sorting) of the clasts 2016/3/31 Analisis Batuan @ Rosana 2016 16 DESCRIBING BRECCIAS When describing breccias, the following features chould be noted : 4. Alignment, imbrication, or grading, and any textures such as “ flow structures” are apparent in the matrix 5. Whether the breccia is clast supported or matrix suppported 6. The ratio of clast to matrix; e.g. Jigsaw; crackle; breccias have a high cement ratio of clasts to matrix, but clasts are separately by a cement of secondary minerals, and are therefore matrix-supported 2016/3/31 Analisis Batuan @ Rosana 2016 17 DESCRIBING BRECCIAS When describing breccias, the following features chould be noted : 7. The nature of matrix: crystallline, clastic, or igneous, and its mineralogy, and whether any open voids are present 8. The relative timing of brecciation and veining. 9. If the breccia is altered or mineralized, whether th matrix and clast seem to have been altered in the same way 10.There could be more tha one generationg of brecciation 11.Sufficiently large exposure is asscesble 2016/3/31 Analisis Batuan @ Rosana 2016 18 SEVERAL DESCRIPTIVE • Crackle Breccia • Jigsaw Breccia • Cockade breccia 2016/3/31 Analisis Batuan @ Rosana 2016 19 DESCRIPTIVE NAMES FOR BRECCIAS (Davies, et al,1995; Davies, 2000; Davies, 2005) based on the approach to volcanics rocks of McPhie et al, 1993 1) Geometry ▪ eg. Pipe, cone, dyke, vein, irregular, tabular ▪ Contact-sharp, gradational, faulted, irregular, planar, concordant, discordant 2) Grain size (clast) ▪ Mud (1/16 mm) ▪ Sand (1/16-2 mm) ▪ Breccia/conglomerate Fine grained (2-4 mm) Medium grained (4-64 mm) Coarse-grained (64-256 mm) Very coarse grained (>256) 2016/3/31 Analisis Batuan @ Rosana 2016 20 DESCRIPTIVE NAMES FOR BRECCIAS (Davies, et al,1995; Davies, 2000; Davies, 2005) based on the approach to volcanics rocks of McPhie et al, 1993 3) Component : Clasts - Matrix - Cement - Open space or vugs a) Clasts ▪ Monomict or polymict ▪ Lithology/type-lithic (type), vein, breccia, juvenile magmatic, accretionary lapilli, pseudoclastic, mineralised, altered) ▪ Morphology – angular, subangular, subround (eg. Pipe, cone, dyke, vein, irregular, tabular) b) Matrix Rock flour, crystal fragments, lithic fragments, vein fragments Texture – banded, laminated, massive 2016/3/31 Analisis Batuan @ Rosana 2016 21 DESCRIPTIVE NAMES FOR BRECCIAS (Davies, et al,1995; Davies, 2000; Davies, 2005) based on the approach to volcanics rocks of McPhie et al, 1993 3) Component : Clasts - Matrix - Cement - Open space or vugs (cont’d) c) Cement ▪ Ore and gaunge mineralogy, and grain size ▪ Texture – e.g. cockade, massive, drusy ▪ Crystalline igneous rock d) Open space or vugs 2016/3/31 Analisis Batuan @ Rosana 2016 22 DESCRIPTIVE NAMES FOR BRECCIAS (Davies, et al,1995; Davies, 2000; Davies, 2005) based on the approach to volcanics rocks of McPhie et al, 1993 4) Internal Organisation (outcrop scale features) ▪ Clast abundance –clast/matrix/cement supported ▪ Clast distribution – jigsaw-fit, insitu rotated, chaotic ▪ Massive (non-graded) or graded ▪ Clast sorting –by size and/or shape ▪ Stratified or unstratified 5) Alteration ▪ Clast/matrix/cement and paragenesis 2016/3/31 Analisis Batuan @ Rosana 2016 23 2016/3/31 Analisis Batuan @ Rosana 2016 24 2016/3/31 Analisis Batuan @ Rosana 2016 25 2016/3/31 Analisis Batuan @ Rosana 2016 26 2016/3/31 Analisis Batuan @ Rosana 2016 27 2016/3/31 Analisis Batuan @ Rosana 2016 28 2016/3/31 Analisis Batuan @ Rosana 2016 29 2016/3/31 Analisis Batuan @ Rosana 2016 30 2016/3/31 Analisis Batuan @ Rosana 2016 31 2016/3/31 Analisis Batuan @ Rosana 2016 32 2016/3/31 Analisis Batuan @ Rosana 2016 33 2016/3/31 Analisis Batuan @ Rosana 2016 34 2016/3/31 Analisis Batuan @ Rosana 2016 35 TUGAS KELOMPOK • Buat kelompok masing-masing anggota kelompok maximal 5 orang. Laporan di ketik 2 spasi. Dan kumpul mgg dpn • Buat tulisan lengkap tentang breksi berikut (1-7) dan beri gambar dan contoh mineralisasi/deposit yang memiliki tipe atau jenis breksi tersebut I. Instrusive Breccias II. Volcanic Breccias III. Phreatomagmatic Breccias IV. Magmatic-Phreatic Breccias V. Phreatic Breccias VI. Tectonic Breccias VII. Sedimentary Breccias 2016/3/31 Analisis Batuan @ Rosana 2016 36