T»p dii DlA CHAT, kat A s6340. l-2gOI4. a. 37-45
DAC DIEM KHOANG HOA SERIOT VUNG SON BINH, HUYEN HU^ONG SON, TINH HA TINH, MOI LIEN QUAN Vdl
CAC PHA MAGMA, KIEN TAO KHU VlTC
NGUYEN THI THANH THAO, NGO XUAN THANH Trudng Dgi hoc Md - Dia chdt. Ddng Nggc TH Liem. Hd Ndi
Tdm tdt: Tu khodng sericit San Bmh khu vuc Huong Son (Hd Tmh) Aipc nghien cdu vi dgc diim dia ch^ thgch hpc, hinh thdi khodng v ^ ciiBg nhu ludi hmh thdiih Kit qud nghien cuu cho thdy sericU tdp trung thaih cdc ddi cd chieu day khoaig 5-10 m, phdt triin Iheo phuangcua cdc dut gov TB-DN, idngchiiuddy cua tu khodng len tdi 50-150 m Tv khodng tgo Ihdnh cdc ddi bien ddi tir ngheo sericit cd dp hgt nhd den Mi gidu sericit cd dp hgt Idn. Kit qud xdc dinh tudi K-Ar cho thdy cdc khodng vdt sericit Aipc hmh thdnh vdo khodng 130-110 Tr.n trudc day vd chung liin quan den cdc pha magma hin tgo thai ky Jwa -Creta trong khu vvc. Chinh logt ma^ mupn hmh thdnh Irong giai dogn ndy da Idm biin ddi cdc dd CO han cua hi long Dong Trau (tudi Trias gida) dpc theo cdc kinh d^ Id cdc dul gdy CO irudc tpa nin ddi gidu sericit. Td hpp khodng vgt Irong cdc ihdn khoaig cho Ihdy khodng hda sericit xdy rad nhiit dp khodng 200-25(fC. cd bift cd nhiing nai gdn kinh ddn nhift dich tgo ddi epidot hda cd nhiit dp len tdi 250-27ff'C.
NhOng ndm gin day, Nganh Dia chit cua nude ta dd phdt hien tu khoang sericit viing Son Binh, huy|n Huong Son, tinh Hd "nnh, ty khodng da dupe tham dd, ddnh gid tiir lupng. chit lupng [7]. Tuy nhien, den nay c h i a cd cdng trinh nghien cihi chuyen sdu ve ddc diim khodng hda sericit, ngudn gdc ciing nhu qua trinh thanh tgo ctia chiing lien quan din thdi ky magma vd kiin tgo khu vuc. Trong bdi bdo nay, dua tren c o sd sd lieu phdn ti'ch ddc diem dia chit khu ty khodng. thgch h(?c. hinh thai khoang vat sericit (phdn ti'ch dudi kinh SEM) vd dinh hidi bdng phuong phap K-Ar d i ludn gidi ddc diim khodng hda sericit vung San Bmh, huy?n Huong Son, tinh Ha Tuih vd moi lien quan cua chiing vdi cdc pha magma kiin tgo khu MIC.
I. G i d THI$U
Sericit Id khoang chit cdng nghiep, dang dupe khai thdc d nhieu nude ti^n thi gidi. Sericit cd tinh chit ddc bift nhu:
nh?, deo, cdch dien, khdng thim nutjc, khdng dpc, tta vdi cdc mdi trudng hod chat, ngdn dupe cdc tia tir ngogi vd tia eye tim, vi vgy dupe sir dyng rpng rdi tirong nhieu ngdnh cdng nghifp nhu polyme, son, mf phim, gdm sit, v.v... Nhimg nude khai thdc vd sdn xuit sericit hdng diu thi gidi Id Trung Qudc, Nga, My. Hdn Qudc, Canada, Phap, Dai loan, Malaysia, Brazil.
Mehico, An Dd vd Srilanca [I. 2, 3, 4, 5, 6]. Mpt sd hdng san xuit cd tiing tren thi gidi nhu: Shanshin sericit, Myoshi Kasei, Nikko Tor>o (Nhgt), CAS for cosmetics (Hdn Qudc), Chuzhou Grea Mineral, Mitsui China (Trung Quoc)... d nude ta, sericit Id logi khodng sdn mdi phdt hifn.
ddc ddo, cd gid trj kinh ti.
37
mu
^czi
caticUi^ 1 IMimi.tw^|-iiaH>W4i«,,i,t^.
r i i|i'ji»»cfc<««rt
^ M ' M t t r U i l l a i i a d i i l . .
^ • n f t t t i w o k l
H nkit»i|Mi:rii«dnr>|i«..
I Bd^Slaiailiil
Hinh 1. 5^ dd dia chdt khu tu khodng
II. BAC DI^M D|A CHAT KHU VI/C
Viing nghien cuu nim ttong ddi ciu tiiic Hodnh Son tiiupc dai tao niii Trudng Son. Cdc dd ciu tfidnh nen ddi ciu ttiic gom ttam ti'ch lyc nguyen, lyc nguyen phun ttdo h? tang Sdng Cd. h? ting Huil Nhi. h? tang Ddng Triu. h? ting Mudng Hinh vd cdc ttam ti'ch D? tii; dd xdm nh|p bao gom cdc phiic h? Sdng Md. Phia Bloc. Bdn Muong [7, 8, 9].
Cdc da ciia h? ting Sdng Cd (O3-S2 sc) phdn bo khd rdng vdi tfidnh phin vgt chit tuong doi dong nhit. chii yiu gim cdc tram tich lyc nguyen dgng flish bi biin chat yiu. H? ting Hudi Nhj (S4 - D, hn)
sericit San Binh - Huang San, Ha 77nh CO tfidnh phin chu yiu Id cdt kit, dd phiin s6t, bpt ket, cdt kit, dd phiin thach anh sericit.
H? ting Ddng Triu ndm khdng chinh hpp tren cdc thdnh tgo c i hon vd dupe chia thdnh hai phan hf ting: a/ Phdn hf tang dudi (T2 a dt,) chu yiu Id cdc dd phun trdo ryolit, cupi kit tuf, tuf lyolit, cupi^ ket thgch anh. Chiiu ddy cua phdn hf tang dudi 250-950 m ; b/ Phdn hf ting tren (T2 a dts) gdm chii yiu Id bdt kit, dd phiin s^t mdu nau, ndu phdt tim, phdn Idp mdng, xen cdc Idp mdng cdt, sgn kit mau xdm nau. Chiiu d4y ciia phdn hf tang 700-800 m.
38
Cac thdnh tao hf ting Mudng Hinh (J mh\ 1§ d phia Ddng viing nghien ciiu, phu bat chmh hpp len cdc da cua hf ting Dong Tr&j, thanh phin gdm cudi kit, sgn ket, cdt kit, phun tiao axiL Phu ien tren la cdc tfianh tgo ti&n tich Df tii gom cat, bpt, set lin cac thiu kinh cudi.
Trong vung nghien cihi cd mat cac tfianh tgo magma xdm nhap phiic he Sdng Md pha 1 (•)rtT2 sm,), tfidnh phin gim dd granit dgng porphyr Id ra d phin Tay Nam cua vung. Phiic he Phia Bioc pha 1 (yaTan pb,) Ip rdi rac d phia E)dng viing nghien cihi, gom cdc thdnh tgo granit sIm mau, granit biotit, granodiorit. Phuc hf Ban Mudng Id ra vdi dien ti'ch nhd d phia Ddng viing n ^ e n cuu, chiing bao gdm
H
da tfiudc pha 1 (yiJ-K bm,), tfidnh I gdm granit amphibol dgng porphyr, granophyr vd cdc dai mgch apht, pegmatiLTrong viing nghien cihi phat tiiin chii yeu hf tfidng diit gdy tfieo phuong TB- DN v<ji gdc ddc khd Idn (60-70°). Cdc hf tfiong dut gdy nay khdng chi ciu tiiic dja chdt vd ddng vai bd Id dudng dan ciia cdc thdnh tgo magma cung nhu dai qudng hda tiong vung. Cdc than khodng sericit tiong viing ciing phan bd tfieo phuang cua hf tfidng diit gdy chinh nay. Ngodi ra cdn
'^-..^Qti.^S^^E^r.'.v
xuat hifn mpt sd lupng nhd cac dut gay d kinhtuyiiL
in. DAC DI^M THANH P H A N V A T C H A T TRONG DOI KHOANG H 6 A SERIC'IT
Trong viing nghien cuu da xdc dinh mdt ddi khodng hod sericit keo dai tfieo phuong TB-DN, dai hon 4.000 m, ipng 50^150 m phat trien trong cac da ttim tich, tram ti'ch phun trdo axit - trung tinh thudc phan he tang dudi cua hf ting Ddng Trdu. Ddi khodi^ hda nay phat triin song song vdi hf tfidng dirt gay chinh ttong vung tfieo phuomg TB-DN, ddi qudng ndm trpn tinng da ryolit cua he ting Ding Trdu. Ham lupng sericit trong ddi khoang hoa bien ddi tir 10 - 60%. Tren co sd phdn ti'ch kiin tiiic, ciu tao vd tfidnh phin tfiach hoc ctia cac miu nghien cuu, khu md cd the chia ra cac dtii sau:
Ddi dd phun trdo bi sericit hoa yiu:
Dd cd kien tnic ndi ban, nin felsit hat nhd hodc tfiuy tinh. Trong miu tfiiy cdc cdu tao dinh hudng, ciu tgo ddng chdy nguyen tfiiiy cua da ryolit hf ting Dong Trau, cac ciu tao ndy bi chia cdt bdi cac ddi phiin hda >iu tfieo phuong TB-DN.
Thanh phin khoang vat chinh gdm tfigch anh (30^^ %), felspat (5(K60 %), UUt + seridt (1-3 %), kaolin (1^2 %). Rdt it khodng vat qudng.
t^h toTxh^ -^ "" '*^* f ^ '"^^ "^ "'"'^ "-""^ ^ biin ddi sericit mgnh. (a) Khoang vgt sencil va pyrophylU chti yeu tdp trung a cdc ddi hep bi biin dang
mgnh xenke vm cgc dai gidu thgch anh. (b) Trong cdc ddi gidu sericit cd cdcZT thgch anh .xuyen len sau vd cdc hgt felspat bi thax thi bai sericit
I Fs; felspat. Ser; sericit. Pyr: pyrophylit. CM: clorit. Qtz: thgch anh).
Ddi biin ddi sericit hoa mgnh: Cac ddi bien ddi sericit hda mgnh tap trung chu yiu d than khodng chinh. Than khoang cd chiiu day K5 m, ca biet cd dogn day tren 16 m, ham lupng sericit tiung bmh 3 0 ^ 0 %, cd mdu dgt tren 70 %. Da cd kiin tnic vi vdy hgt biin tinh (ndi ban tan du, nin vi felsit tdn du), ciu tgo phdn dai, phdn phiin mgnh, cac khodng vat cd tinh dinh hudng rd rdng, tfianh phin khodng vat gdm thach anh (33-35 %), felspat (3-5 %), sericit khd Idn ( 3 0 ^ %). pyrophylit (10^12 %).
epidot xuit hifn tixing mdt sd miu. chiim 1-2 %. Khodng vdt qudng chii yiu Id chalcopyrit (1-2 %) (Anh la).
Ddi biin ddi pyrophylit hda yiu: Cdc ddi bien doi ndy tgo nen cdc tfidn khoang hfp keo ddi song song vdi nhau va vdi tfidn khodng chinh. chiing xuit hifn ttong mpt ddi rpng khodng 30-40 m. Cdc tfian khodng bj phdn phiin khd mgnh. Dudi kinh quan sdt tfiiy mdt sd kiin ttTic ndi ban cua dd ryolit van cdn tdn tgi dgng bi gdm mdn tfiay tfii. nhu ban tinh felspat bi bien ddi sericit yiu. mdt sd hgt bj kaolinit hoa. phan nin bi kaolinit hda vd clorit hda yiu. Thdnh phin khodng vgt gdm tfiach anh (40^-50 %). fdspat (30H-40 %). sericit (10^15 %). pyrophylit (10^25%) vd it kaolin (1-5 %). Khodng vgt qudng chii yeu Id chalcopyrit (-1%) (Anh lb).
Cdc tfidn khodng sericit tixing khu vyc phdt ttien tfieo phuong TB-DN, ddc vi phia TN vdi gdc doc khodng 65-70°. Cdc tfidn khodng chinh gidu seridt. bj mylonit vd bien dgng mgnh. Cac ddi mylonit chiia tfidn khodng ndy cd dgng h^p. keo ddi. ra xa din tfidn khodng dd bj phdn phiin yiu den gin nhu khdng bj phdn phiin. Cung vdl sy bien mdt cua ddi mylonit tfii hdm lupng cdc khodng vgt sericit cung gidm dan, ra xa tfidn khodng tfil sericit gin nhu vdng mdt md chi cdn khodng vdt biin chdt ilht. Ddy Id minh chimg id rdng cho qud
tiinh sericit hda tiong cdc da hf ting Ddng Trau phan bd dpc tiieo cdc ddi phd hiiy diit gay kiin tgo phuang TB-DN tixing vimg, Cac diit gay nay xuit hien tiudc cdc hogi ddng tgo khoang va ddng vai tid nhu mot kenh din ddng nhiet dich tii dudi sdu di len gay biin chit (sericit hda. clorit hda v4 epidot hda) da xung quanh.
ly. BAC B | £ M KHOANG H 6 A , HINH THAI K H O A N G VAT SERICIT
Td hpp cpng sinh khodng vdt biin chat ttong cdc tfian khoang khu vyc nghien ciiu gdm tfigch anh + sericit ± illjt + pyrophylit ± epidot -i- clorit + chalcopyrit dien hiiih cho logi sericit hinh tfidnh lien quan din nhift dich. Trong ddi khodng hda. mpt sd nai xuit hien cdc mgch aplit, cdc mgch tfigch anh ciing la nhihig bdng chiing rd rang cho sy cd mdt ciia cdc ddng nhift djch xuyen Ien ttong khu vyc. Qud ttinh sericit hda tii cac hgt khodng vgt felspat vd mdnh tfiiiy tinh nguyen tfiiiy ciia cdc trim tich phun ttdo hf ting Ddng Triu dupe quan sdt rit rd dudi kinh hiin vi phan eye, qud ttinh biin doi dd cd tfie Idm thay dii hodn todn hinh dgng nguygn tfiiiy ciia khodng vat hodc mdnh tiiiiy tinh nguyfn thuy, nhung trong mdt so mau cdn tdn tgi mpt s6 khodng vat felspat chua bj bien ddi hoan todn vd cdn giii Igi mpt phan trong dd gdc. Sy tfiay ttii khodng v|t sericit tren cdc khodng vgt felspat hodc manh thuy tinh thuong di kfm vdi hifn hrpng clorit hda vd epidot hda, diin hinh cho kieu biin doi nhift dich nhift df tfiip den tmng binh. Ddc bift, quan sdt trong nhieu ldt mdng tfiiy cd sy xuit hifn ciia cac mgch thgch anh nhd khdng bj bien dgng hoac biin dgng yiu, khdc bift hodn todn vdi thgch anh mdnh vyn sdc canh nam lan Ipn vdi khodng vgt sericit ttong dd, chiing td day Id nhOng mgch tfiach anh the hf sau dupe hmh tfidnh do sy xuyfn len ciia cdc ddng nhift djch ciia magma 40
dudi sau ho$c bdn tfian chiing la san jAim do gidi phdng silic tixmg qua ttinh bi&i ddi sericit hda. Nhiing quan sdt tten hoan todn phii hop vdi cac nghien cihi ttudc day ve biin ddi sericit tiiay tiii khodng vat felspat hodc mdnh vyn thuy tinh trong da axit phd bira tren thi gidi, nhu sericit phdt ttiin tt^n da granit khu Rosses cua Ai Len [5], khdi xdm nhap granit Skidoo, California (My) [1]. Tii nhihig quan sat va so sdnh tren cho phep nhdm tdc gid xac dinh ring cac ddi sericit hda d khu tu
khodng Huong Son, Ha Tuih dupe hmh thanh do qua trinh biin ddi nhiet djch cua cac da magma gidu chit bdc vi sau tac dpng len cac da gidu felspat cua he ting Ddng Triu. Cac dong nhift dich hdu magma lien quan din cdc da xam nhgp granittiid tfiudng cd ham lupng kali cao, chiing di vao ttong cac da trim ti'ch phun trao cik hf ting E)dng Triu thdng qua cac kenh din la cac ddi pha huy, dut gay kiin tao vd lam biin ^ i sericit hda (kali hda) cac khoang vat felspat cd trudc.
Anh 2. Hinh dnh cdc khodng vgt sericit Khodng v$t sericit dirpc quan sdt d muc dp phdng dgi Idn dudi kinh hiin vi difn tii quet (SEM). Hinh dgng va kich tfiudc cac khodng vgt sericit trong cac mau quan sat cho thiy chiing kha da dang, bao gdm dgng tim ddng thudc vdi kich tfiudc hgt Idn khodng tir 10-20 ^m (hat Idn), logi 8-5 pm (hgt trung bmh) vd logi cd hgt nhd dudi 3 pm. Trong cdc mau a din bien chit sericit hda, cdc khodng vdt kich tfiuDC Idn, nhd va tiimg bmh ddng tfidi xuit hifn va cd sy lin Ipn. Trong cdc ddi bien chit tfiip hon, kich tfiudc hgt sericit tfiudng ttung bmh din nhd. Phin Idn cdc khodng vdt sericit cd dgng gdc cgnh, khdng cd djnh hudng. Mpt sd miu quan sat tfiiy khodng vgt sericit cd tinh djnh hudng theo mpt dai hep trong miu, cd 15 day Id nhiing phin bi tai sdp xip djnh hudng do cdc hifn tirpng diit p y , biin dgng vi sau (Anh 2). Nhu vdy kich
dudi kinh hiin vi dien tir quel (SEM).
tfiudc vd hinh dgng cua khoang vat sericit phy tfiupc vao miic dp biin ddi ciia cdc ddi bien chdt, cd le loai sericit hat Idn Id nhihig phin biin ddi gin kenh din cua cdc ddng nhift dich di len d diiu kifn nhift dp cao hon vd gidu vdt chit de gdy bien ddi han ttong ddi pyrophylit hda.
V. XAC B|NH TU6l K-Ar CHO KHOANG VAT SERICrT
Di }iac djnh tiidi tfianh tao cdc khodng hda sericit hien nay, tren tf^ gidi tfiudng su dyng phuong phdp dinh tiidi K-Ar hodc ^'Ar/^^Ar tien chinh cdc mau tach tiiyen sericit tii phdng tfii nghifm. Phuong p h ^ nay da duoc sii dung khd nhieu va cho nhiiu kit qua cd chit lupng vd dgt dp chinh xdc cao. Miu sericit diing di djnh hidi dupe Idy tiong cdc tfidn khodng cd hdm lupng swicit cao (60-70 %) diing di phdn tich hidi tiiyet ddi bdng phuong phdp
K-Ar tgi Trudng Dgi hpc Khoa hpc Okayama Nhdt Ban. Do kich tfiudc hgt sericit nhd nfn dp hat dupe sir dyng dk dua vdo hiyin liy dudi 100 pm. Phuang phdp tdeh Ipc sericit dupe chiing tdi sii dyng tfieo phuong phap tdch ttpng lyc ttong cac binh tfii ti'ch 2 lit, tudn tfieo nguyen ly ling dpng Stokes ttong diiu kien nhift dp phdng dupe giu dn djnh 20-24°C. Qua ttinh tach Ipc khodng vat vd cdc budc phdn tich dd dupe md td chi tiit ttong [2, 6].
VI. K^T QUA XAC BjNH TU6l VA LUAN BAN ye KHOANG H 6 A SERICIT VUNG SOTN BiNH
1. Tu&i tgo khodng sericit
Kit qud xdc djnh tiidi dupe tiinh bdy nhu Bdng I. Nhu dd md ta d ttfn, cdc khodng vdt sericit ttong cdc ddi biin chit cua cdc tfidn khodng cd kich tfiudc tfiay ddi, qua phdn tich cd hgt cd tfii tfiiy cd 3 cd hgt chiim s i lupng Idn: Logi Idn tfiay doi tir 10-20 pm, logi 5-8 pm vd logi cd hgt dudi 3 pm. Sericit Id khodng vdt hinh tfidnh tfidng qua biin ddi ciia ddng nhift djch gidu H2O (vd cd tfii K) tde dpng Ien
mii Ilia axit, qud ttinh biin ddi ndy tgo noi cdc hat sericit cd kich tfiudc hgt tii Idn din nhd, phy tfiupc vao nhift dp tdc dfng Thdng thuimg, qua ttmh biin dii nhift djch nay dien ra tixing giai dogn ddi lifn quan den cdc pha magma dudi sdu ciing nhu toe dp ngudi lgnh cua chiing vd tfidnh tao nen tfian khoang sericit bao gim nhifu tfie he khoang vgt. Chinh vi v^y, ttong miu xdc djnh hidi seridt chiing tdi dd chia miu tfianh 3 ca hgt khdc nhau (Bang 1) nhdm xac djnh chinh xdc cdc pha tfidnh tgo chinh cua qudng seridt ttxmg viing tu khodng.
Ket qud xac djnh hidi cho kit qui hidi tfiay doi tii 130,1±2,9 Tr.n ddi vdi miu cd hgt 10-15 pm, I25,7±2.8 Tr.n ddi vdi miu cd hgt 5-8 pm vd 117.9±2,8 Tr.n dii vdi miu cd hgt 1-2 pm. Kit qud xdc djnh hiii sericit bdng phuang phdp K-Ar dd dupe xdc djnh vd ling dyng cho kit qud ttii dang tin c§y cho rit nhiiu nghifin cihi ttfn the gidi [3.4]. Kit qud djnh hidi ciia nhdm tac gid cho ph6p chiing tdi khdng djnh ring hioi tfidnh tgo ciia cdc khodng v§t sericit frong ty khoang Son Binh tfidnh tgo ttong khodng tfidi gian 130.1-117.9 Tr.n, hrong ung vdi tfidi ky Creta sdm.
cdc khodng vgt felspat vd cdc fliuy tinh
Bdng 1. K4t qud phdn tich tu6l K-Ar khoang, y j t sericit Tuil K-Ar
2. M 6 | liin quan gifra thdnh tgo qufng vd cdc pha magma - kiin tgo khu v ^
Kit qud nghifn ciiu ndy cho tfiiy, tfidi ky tfidnh tgo ty khodng sericit tit muOn so vdi logt magma hmh tfidnh lifn quan din 42
chu ky kiin tgo tgo mii Indosini ttong khu vyc hiii Permi - Trias. Kit qud hiii Creta sdm hinh tfidnh nfn qudng sericit ttong vimg hodn todn ttimg hpp vdi logt magma kiiu kiim - vdi din cao nhdm lifn quan
den dieu kifn kiin tao hiit chun/va chgm hmh tfianh rdng rdi d khu vuc Nam Trung B^ va Nam Bd cua Vift Nam, chiing bao gdm logt andezit - dacit - lyolit Bao Loc - Nha Trang (129-100 Tr.n). logt gtanibiid Djnh Qudn - Deo Cd (92-109 Tr.n), dacit - ryolit hen quan xdm nhgp granit hai mica, granit biotit ciia logt Ban Duong (76-100 Tr.n)... [8, 9]. Trong vimg nghien ciiu, cdc da ryodacit xuit hifn tixing bdn titog Mudng Hinh, cdc dd xdm nhgp granit chiia amphibol, granit hai mica dgng porphyr, granophyr va cdc dai mgch aplit, pegmatit ciia phiic he Ban Mudng cd tudi dupe xdc djnh la Jura mupn din Creta sdm. Logt magma granit vdi ddc tiimg
^ nude va nhdm (chua amphibol, muscovit) lien quan din cdc dai mgch pegmatit, aplit xuit hifn khd phong phii trong khu vuc cho tfiiy hogt dpng hau magma nhift djch lien quan din cdc magma xdm nhgp xdy ra khd mgnh raS, vd hifn tupng sericit hda cac khodng vdt felspat bit diu xdy ra khodng 130 Tr.n, kfo ddi din khodng 117,9 Tr.n tiirdc ddy.
Nhu v^y, cd tfii hieu qud ttinh huih tfidnh qudng sericit frong khu vyc md nghifn cihi lifn quan den logt magma gidu chit boc hinh tfidnh vdo Jura mupn din Creta sdm. Trong giai dogn tgo mii Indosini, logt magma ttong khu vyc nhu phirc hf Sdng Ma, Phia Bioc vd logt ttim tich - phun trdo ryolit hf ting Ddng Triu dupe hmh tfianh. Sau khi dupe hinh tfidnh, cdc pha tgo mii Indosini ciing nhu nhChig hogt dpng dja chit vi sau lam biin dgng, biin cdi chiing. Cdc diit gdy cdt qua cdc thdnh tgo dja chit ndy xuit hifn trudc tgo khodng sericit va ddng vai ttx) nhu mpt
kenh din ket ndi cdc vat chit dudi sau vtii phin vd ndng phia tten. Trong giai dogn tao mii Jura mupn Creta sdm, logt magma xam nhap axit din a kiim xuit hien ttxmg khu vyc (phiic he Ban Mudng) ddng thdi cac phim ttao ryolit khu vuc Idn can (khu vyc bdn tiling Sim Nua). Sy xuat hifn ciia logt magma axit din d kiim nay la diiu kien fliuan Ipi di hmh tfianh cdc ddng nhiet djch hau magma. Cdc ddng nhift djch nay xuit hifn tir cac vdm magma sau ben dudi vd tfieo cac kf nh ddn la nhimg diit gay phd huy cd ttirdc di di Ien phia ttrai. Khi nhOng ddng nhift djch nay gap cdc da tfiuan loi (gidu felspat) se xdy ra phdn iing tfianh tao sericit tfieo cdng thirc:
Felspat -I- H2O (+K^ = sericit + Si02 (+ K2O niu felspat tfiupc nhdm gidu K)
Trong khu vuc, vdi sy cd mdt gidu cdc khodng vat felspat hodc vat chit thiiy tinh cua hf ting Ddng Triu la diiu kifn tfidn Ipi di tfidnh tgo tu khodng sericit. Nhu da md td tren, cdc thdn khodng sericit frong viing phdt triin theo cdc ddi dut gdy, cdc ddi mylonit hda vd cd sy phdn ddi biin chat cao hon tit ttimg tam ddi diit gdy vd gidm din din da gdc khi din xa ddi dirt gay, day ciing Id bdng chiing cho tfiiy ddng nhift dich thudc pha magma mufn xuyen len theo cdc diit gay di tgo nfn cdc phan ling tgo khoang sericit ttong vimg.
3. Oidu kifn nhigt d$ thdnh tgo qu$ng Theo cdc nghien ciiu ttirdc ddy. sericit tfiudng dupe tfidnh tgo trong khodng nhift dp tir 175 - 350''C. Tiiy tfiudc vdo nhift dp thanh tgo t i hpp cpng sinh khoang vdt ttong quang se cd sy tfiay doi. dua vdo to
. ^ ^ H hpp c^ng sinh khoang vat se cho chiing ta
biet dupe nhift dp thdnh tao ciia da.
Thdng tfiudng ddi vdi logt biin chit khdng cd sy xuit hifn ciia khodng vat biotit se cho nhiet dp biin chit dudi 300°C. To hop cpng sinh khoang vat cho tfiiy ddi khoang hda gidu nhit ddc tiimg td hpp biin chit thgch anh, sericit, pyrophylit. clorit-^kaolmit vd khoang vat q i ^ g chalcopyrit, diin hinh cho nhift dp biin chit khodng 200 - 250''C, ttong mOt sd miu cd sy xuit hifn cua epidot tfii hifn diiu kifn biin chit cd tfii len din 250 - 300''C, cd le day la nhihig bd phdn nhd ndm gin kenh din nhift djch. Ti hpp khoang vgt ttong cdc ddi khodng hda yiu gim illit, sericit, clorit+kaolinit tfii hifn qud ttinh biin chit xdy ra d phin ndng cua vd Trdi dit.
VII. KtT LUAN
Tii nhiing kit qud nghien ciiu vd ludn gidi tt^n, nhdm tdc gid cd nhihig kit ludn nhu sau:
Cdc tfidnh tgo magma ciia phuc hf Sdng Md ttong khu vyc Id logi magma gidu nhdm, cd tiiii hinh tfidnh vdo cuii Trias mudn (T,)', hrong ung vdi pha tao mii hidosini Idm ddy vd Trdi dit.
Cdc khodng vgt sericit trong ty khodng sericit Son Binh, Huong San Hd Tinh cd kich tfiudc da dgng, tupng trung Chung gim 3 cd hat co bdn: 10-20 Itm. 5-8 pm vd logi c6 hgt dudi 3 pm.
khoang tfidi gian tir 130 - 118 Tr.n ttudc day. Chiing lien quan din pha magma kifn tao vdo Jura mupn Creta sdm, hrang iing vdi giai dogn tgo mii Yin Son!
Sy tfianh tgo cua ty khodng seridt vimg nay lien quan den dung djch h§u magma cua logt magma granit tir kiim vdi den granit hai mica va cdc dai mgch aplit, pegmatit ciia phiic he Bdn Mudng (tudi J3-K1).
Qud tiinh biin ddi nhift djch cdc khodng vdt felspat va tfiiiy tinh ntii lua tixing dd ciia hf ting Ddng Triu chii yiu tap tiimg dpc flieo cdc dirt gdy phuong TB-DN.
VAN L i f u
!• Collins, Lorence G., 1997. Sericitization in tf,e Skidoo Pluton, California: a possible end- stage of large-scale K-metasomatism.
Cglifornia Stgge University Northridge 19pp. ISSN 1526-5757
2. Itaya T., Nagao K., Nishido H.
and Ogata K., 1984. K-Ar age determination of Late Pleistocene volcanic rocks. Journal of Geology Society of Jgpan, 90, pp. 899-909
Ty khodng sericit Son Binh, Huong Son, Hd Tmh dupe hinh tfidnh ttong
'Jljf''^.granUpMc hf Sdng Mdtheo Idi lifu ndi Id Trias gUhi (BBT).
3. EsnRL D.D., SnoooN J., MrNccnou LBn, Conau P.H.N., Nonrnnop H.L, 1987. Sericite from tfie Silverton caldera, Colorado: Corrdation among sttuchue, composition, origin, and partide tfiickness. American Mineralogist 72, 914-934
4. Nabetani A., Shikazono N., 2002.
Chemical process and environment of hydrotfiermal alteration of acidic volcanic rocks in tfie Mitsuishi disttict, soutfiwest 44
Japan. Geochemical Journal, Vol. 36, pp. 19-38 Cm Japanese mth Endish abstract) 255-269
7. Nguyen Van Can va nnk, 2011.
5. Medzno Que and Alstam R. Alle, "Bao cao thdm dd md sericit khu Son Trd, 1996. Sericitization of plagioclase in tfie ''">'?" Huong Son, tmh Ha Imh"
Rosses Granite Complex. Co. Donegal, 8. Trin Van Tri, Vn Khuc (Ddng Chd Ireland. Minerglogical Magazine, 60, pp. ^'^") ^^ ^"^ 2009. EHa chit va Tai nguyen 927-936. ^^^^am. Nxb Khoa hoc Tu nhien vd Cdng
nghe. HdNpi, Viet Nam, 589tr.
6. Nagao K , Nishido H., Itaya T. and , T^„ V S T • A/- i ^ . ^ . . Ooata If io«4 A J-* , • * " " * " ° ^ n . Vu Khuc (Eds), O ^ t a IC 1984. An age dderminatton by 2011. Geology and earth resources of Vift K-Ar metfiod. Bull. Hinizen Researdi Nam. Pulishing House for Science and Institute, Okayama Univ. Sci, No. P, pp. Technology. HdNpi. Viet Nam, 645pp.
SUMMARY
Characteristics of sericite mineralization in Son Binh area, Huwig SOT district, Ha Tinh Province, its relation witfi regional tectono-magmatic phases
Nguyin Thi Thanh Thdo, Ngd Xudn Thdnh Detailed stiidies of geology, pettology, mineral morphology and K-Ar geochronology of sericite fiom Son Bmh sericite deposit (Huong Son, Hd Tuih) show tfiat sericite is concenttated in several zones witfi tfiickness of 5-10 m extendmg in tfie same direction as tfie NW-SE sttiking faults, witfi a total tfiickness of tfie deposit witfim 50-150 m. The deposit consistii of alteration zones ranging fiom fine-grained low- sencite one to coarse-grained high-sericite one. K-Ar age dating suggests tfiat tfie sencitization took place during 130-110 Ma, corresponding to tiie Jurassic-Cretaceous tectono-magmatic phases in tfie region. It is tfiis magmatic series formed in tfiis period tfiat caused tfie alteration of tfie older rocks of Ding TrAu fonnation (aged Middle Tnassic) along tfie preexisting faults w*ich serve as conducting channds. fonning tfie sericite-rich zones. The mmeral assemblage in tfie ore bodies suggests tfiat the sericitization occurred at tfie temperatiire of ca. 200-250»C. exceptionally in some locations near flie hydrofliennal conducting channels epidotization zones were formed wifli temperahue up to 250-270 "C.
Nguai bien tdp: GS.TS Trdn Vdn Tri; PGS.TS Nguyin Vdn Phd.
45