Transcript
RA-06 RA-0 6 : Hydrothermal Brec Breccia cia Texture Texture
HYDROTHERMAL BRECCIA TEXTURE
ROCK S A NA NAYSLIS YSLIS
Piroklastika jatuh j atuhan an
Proses sedimentasi
Kubah lava Leher gunungapi sill
Aliran lava
retas
Volkanisme Kantong magma
Dapur magma
Proses magmatisme
STRATIGRAFI/ FASIES VOLCANIC
(Bog ie & M ackenzie, 1998) 1998)
VOLC VO LCA A N I C B R E C C I A VOLCANIC BRECCIA is pyroclastic pyroclastic (fire-formed fragments) fragme nts) and forms in explosiv exp losive e 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.
BRECCIAS
Breccia is rocks that composed of clast (fragments) (fragm ents) > 2 mm size and angular ang ular nor sub-angular sub-a ngular shape, shape , cement (hydrotermal (hydrotermal mineral or crystalline igneous rock rock)) and open space
Grain-size Grain -size of subdivision sub division of clast are are : 2-4
mm fine-grained
4-64 mm
medium-grained
64-256 mm coarse-grained >
256 mm very coarse grained
Bryner (1968) (196 8) recognized recognized problem when he ppointed out that many clasts in hydrothermal breccia are mostly mostly rounded, so the th e term of “breccia” was was misleading mislea ding in these cases
Breccias
in some some cases ca ses consists of fragments fragm ents that are neither angular nor sub-angular sub-a ngular (e.g. (e .g. Pebble breccia)
GENETIC CLASSIFICATION OF BRECCIAS There are seven principal types of breccia comprising 13 sub-types occuring 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 Breccias
1. INTRUSIVE BREC BRECCIAS CIAS These are subdivided into three members : 1a. Magmatic-Intru Magmatic-Intrusive-Breccias sive-Breccias :
– Created during the emplacement of an intrusive body – Consist of clasts comprising xenolith of country rocks, including previous intrusives, and fr agment of ea rlycry rysstal talliz lized porti rtionw of the intrusive ive disrupted during empl emplaacemen ementt, in matrix of cry ryst staalline igneo neous mater eriial – Frequently occur on the margins of intrusive bodies and contain clast of countr y rock in a crystalline igne igneou ouss matri atrix x
1. INTRUSIVE BREC BRECCIAS CIAS These are subdivided into three members : 1a. Magmatic-Intru Magmatic-Intrusive-Breccias sive-Breccias :
– High te mperature of e mpla ce ment and show react ion rims around und the xeno enoliths
ion in this typ type of brec ecccias is direc ectt magm agmatic atic – Mineralization origin and some re action w ith host rocks as in skarn deposit portaant se settting for base base meta etal minera nerallizat zation – Import tion: the ore-hosting breccia could be – In term of exploratio expected to be closely spatially related to the margins of an intrusive, and these area should be explored.
1. INTRUSIVE BREC BRECCIAS CIAS These Thes e ar aree subdivided sub divided into three members membe rs :
1b. Magmatic-Hydrothermal Breccias 1c. 1c . Magmatic-T Magmatic-Tec ecton tonic ic Breccias Breccias
2. VOLCANIC BRECCIAS BRE CCIAS The essentil feature of these breccia s is that the energy causi using brecciation ion (and/or) ejec ecttion ion from the volcano) is dependent on the release of pressure of mag magmat matic volatiles. Divided into nto two subub-types pes: a) Endo Endoge geno nous us Volcan lcanic ic Brecc Brecciias (no (non-er n-erup upttive ive or vent brec brecci cias as)) b) Exogen Exogeno ous (Erupt (Eruptiv ive) e) Volcani lcanicc Brec Brecci cias as
3. PHREATOMAGMATIC BRECCIAS These are equivalent to hydromagmatic breccias (Sillitoe , 1985). Phreatomagma tism occurs when upwelling magma encounter water. This may be groundwater, connate water, or a body of surfa ce watter wa er.T .Thi hi brec brecccias divided into : a. Endogenous (non eruptive) phreatomagmatic breccias b. Exogenous Breccias
(eruptive)
Phreatomagmatic
4. MAGMA MAG MATIC TIC-PHR -PHREA EATIC TIC BRE BRECCI CCIAS AS
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 h eated by the intrusion of magma magm a
Does
not contain juvenile magmatic products
Divided
into :
Edogenous A. Edogenous
(non-eruptive) Magmatic-Phrea Magmatic-Phreatic tic
Breccias B.
Exogenous (eruptive) Magmatic-Phreatic Breccias
5. PHREATIC BRECCIAS A
phreatic phreatic eruption is caused ca used by expansion of steam and gas from a water-dominated water-dominated fluid, with only a minor component of magmatic magm atic volatiles volatiles
The
mechanism of energy transport to the focus of eruption has to be at a t some point by a freely-conveting freely-conveting column of sub-critical hydrous hydrous fluid
Reffered Reffered
as hydrothermal hydrothermal eruption or vent brecci b recciaa
divided into : A. B
Endogenous Phreatic Breccias
Exogenous Exog enous Phreatic Phreatic Breccias Breccias
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 as sociated with a tectonic breccia in nonmetamorphosed volca can nic terrain, it is unlikely that the tectonism caused the mine raliz ation, and so the function of the b reccia is pro probabl bablyy just ust to pro provide vide per permeable ble path path for miner neralzing fluids uids.. trackin king the extent of the Exploration strategy should cons ist o f tra brec breciia, and sepa eparatel tely inter nterpr pret etiing the miner neralizing proc proces esss eral aliizat zation appears to have pre pre-dat dated fau faulting, the pos possib sibility If miner of co conc nceealed cutcut-o off miner neralized zone shoul hould d be co cons nsiider ered ed..
7. SEDIMENTARY BRECCIAS
in the typical t ypical epithermal/porph epit hermal/porphyry yry environment, environment, they consist principally pr incipally of volcanic vo lcanic material ma terial
volcaniclast astic sediment range from epiclastic deposits such as laharic or avalanche deposit, that have little evidence of sedimentary processes, through through to well-s ell-sorted orted volcanoge olcanogen nic sands sandston tones es or pumicit pumicitie iess
the essential feature of these breccias is that they have been emplaced on the earth’s surfac surfacee by predo predomin minan antl tlyy se sedim diment entary ary proce process sses es..
Features
indicative of water transport may be apparent, suh as cross beddin bedding.T g.Ther heree may may be interb interbedd edded ed non volcano olcanogen genic ic se sedi dimen ments ts
miner mineral aliz izat atiion in this this setti etting ng is not not dir direc ectl tlyy relat elated ed to brec brecci ciati ation on proc proces essses
In
term of exploration, can be apply similar to an exogenous volcanic breccia.
The
exte xtent and and locati ation of the bre breccia can be pre predict dicteed by stra rattigraph aphy, but but the the mine mineral raliz izin ingg proc proces essses should hould be seper eperat atel elyy ev evalu aluaated ted
DESCRIBING BRECCIAS
breccia are very importa rtant host rocks for mineralization, not only bec becous ouse, of the lar arge ge surf urface ar areea they mak akee available ble for for wate ater-ro -rock inte intera ract ctio ion n and the the fac actt that they repr epres eseent zones ones of hig high perm permea eabi bilility ty,, but but some of the pro processes of bre breciati ation such uch as hydraulic frac actturi uring can ca n clos closel elyy relat elated ed to the the proc proces esss of mine minera ralilizzatio ation n
He
class assific ficati ation is bas based on the pro proporti rtions of vein clast ast, rock clasts asts,, chem hemicall ally deposited cement, and clast astic/igneo neous matri atrix x within the breccia.
When de desscr crib ibin ingg brec brecci cias as,, the the foll follow owin ingg feat featur ures es chou chould ld be note noted d: When 1. Clast Clast lithologi lithologies es 2. The shape hape of clas clasts ts 3. The size and and size distribu ributtion (de (degr greee of sorti orting) ng) of the clas clasts ts
DESCRIBING BRECCIAS When
des esccribing 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 suppor ted 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 secondar y mine mineral ralss, and and ar aree the therefor fore matri matrixx-ssuppo upporte rted d
DESCRIBING BRECCIAS When
des esccribing breccias, the following features chould be noted : 7. The natur ture of matri trix: cry rysstal tallline, clastic, or igneous ous, and its mineralogy gy,, and whether any open voids are present 8. The relati ative tim timing of brecciati ation and and veinin ning. 9. If the breccia is altered or mineralized, whether th matrix and clast seem to have been altered in the same ame way 10.There could be more tha one generationg of 10.T brecciation 11.Su 11. Suff ffic icie ient ntly ly larg largee expos xposur uree is ass assce cessble ble
SEVERAL SEV ERAL DESCRIPTIVE D ESCRIPTIVE •
•
•
Crackle Breccia Jigsaw Breccia Cockade breccia
DESCRIPTIVE NAMES FOR BRECCIAS (Davies, et al,199 al, 1995; 5; Davies, 2000; 200 0; Davies, 2005) based bas ed on the appr app roach to volcanics rocks of McPhie et al, al , 1993 1) Geometry eg.. Pipe, cone, dyke, vein, irregular, tabular eg ContactContact-sharp, sharp, gr grada adati tiona onal,l, fault faulted, ed, irregula irreg ularr, plana pla narr, concordant, concordant , discordant ▪
▪
2) Grain size (clast) Mud (1/16 mm) Sand (1/16(1/16-2 mm) Breccia/conglomerate Fine grained (2(2-4 mm) Medium grained (4(4-64 mm) CoarseCoarse-grained (64(64-256 mm) Very coarse grained gra ined (>256) ▪
▪ ▪
DESCRIPTIVE NAMES FOR BRECCIAS (Davies, et al,199 al, 1995; 5; Davies, Davies , 2000; 200 0; Davies, Davies , 2005) 200 5) based base d on the approach to volcanics rocks of McPhie et al, 1993 3) Component C omponent : Clasts - Matrix - Cement - Open space or vugs a) Clasts Monomict or polymict Lithology/typeLithology/type -lithic lith ic (type), vein, breccia, juveni juvenile le magmatic, accretionary accretionary lapilli, lapill i, pseudoclastic, pseudoclastic, mineralised, mineralis ed, altered) Morphology angular, subangular , subround (eg. eg. Pipe, cone, dyke, dyke , vein, irregular irregula r, tabul tab ular) ar) b) Matrix Rock flour flou r, crystal crys tal fragment f ragments, s, lithic lith ic fragments f ragments,, vein fragments Texture banded, band ed, laminate lami nated, d, massive mas sive ▪
▪
–
–
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 C omponent : Clasts - Matrix - Cement - Open space or vugs (cont’d) c) Cement Ore and gaunge mineralo miner alogg y, and grain gra in size Texture – e.g. e. g. coc cockade kade,, massive, massive, drusy Crystalline igneous rock ▪ ▪ ▪
d) Open Open space or vugs
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 Organ isation (outcrop scale features) Clast abundance – clast/matrix/cement clast/matrix/cement supported Clast distribution – jigsaw jigsaw-fit, insitu rotated, chaotic Massive (non(non-graded) or graded Clast sorting – by by size and/or shape Stratified or unstratified ▪ ▪
▪
▪ ▪
5) Alteratio Alteration n Clast/matrix/cement and paragenesis ▪
TUGAS KELOMPOK •
•
Buat kelompok masing-masing anggota ang gota kelompok kelompok maximal max imal 5 orang. orang . Laporan Lapor an di ketik 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 breksi tersebut I.
Instrusive Breccias
II.
Volcanic olca nic Breccias B reccias
III. Phreatoma Phreatomagmatic gmatic Breccias IV. Magmatic-Phr Magmat ic-Phreatic eatic Breccias V. Phreatic Breccias VI. Tectonic Breccias VII. Sedimentary Sedimentar y Breccias Breccias
