I

LAMPROPHYRES IN THE HAGOTA - TULGHEŞ ZONE (EAST CARPATHIANS)

Lucian IONESCU

GEOLEX S.A., str. Korosi es. 7,4100 Miercurea Ciuc

Key words: East. Carpathians. Tulgheş. Lamprophyres.

Abstract: In t.he Hagot.a-Tulgheş zone about 200 lamprophyre veins have been iden­tified, which penetrate mostly the epimetamorphic formation of the Tulgheş Group. AII t.he wells in the area penetrated lamprophyres, amount.ing to 2.27 % of the total length drilled. MosI. of the analysed lamprophyres represent spessartites, oclinites, beerbachites. Vogesit.es, kersantites, malchites anei camptonites are found subordi­nat.ely. The majorit,y of lamprophyres are intensely alt.ered, being affected especially by carbonatations anei subordinately by limonit.izations, chloritizations, serpentiniza­tions , epielotizat.iol1s, albitizations anei argillizations. Locally, they contain enclaves from the metamorphic formations penetratecl ancl more rarely from older syenites anei lamprophyres. Ali lamprophyres occur on fissures. They are grouped in fielcls, within which the position of the veins is relatively constant. Most of the lamprophyre boclies are orientecl after a system of conjugated direct.ions, N-S (wit.h eastern clippings) anei E-vV (with northern dippings). The elistribut.ion of the minor element.s in t.hese rocks cloes not clepencl significantly on the spatial position of the veins 01' on sampling site , it pointing to t.he common origin of ali lamprophyres. In the whole area, the lam­prophyres are founcl in associat.ion with epigenetic mineralisations. This fact can be explainecl by the use of the same access ways. The age of the lamprophyres in the Hagot.a-Tulghe~ zone is probably Upper Jurassic-Cretaceous.

The study zone is situated in the Giurgeu Mts, sout.h of the Bistrieioara River, covering the lower basins of the Asoel, Rezu Mare and Put.na valleys. The geologic setting is dominated by t.he epimeta­morphic formations of the Tulgheş Group, that con­st.ituie the Putna Nappe, developed in the central parI. of a wide antiforl1l (Valea Putnei antiform). The Tg3 and Tg4 format.ions are cropping out. here. Be­t,ween the Asael anei Rezu Mare valleys , clue t.o a secondary t.ect.onic plalle (Asod-Rezu Mare digit.a­bon) , t.he Tg3 and Tg4 suit.e is doubled . In the eastern and sout.hern parts, the Tulgheş Group is overlain by the Salaj Nappe (formed of seriei te­muscovite±biotite±feldspar quartzitic schists) and overlies the Rarău Nappe (formed of diverse me­somet.amorphic rocks and metagranitoids of t.he Bretila Group) (Fig. 1). The metamorphics are pen­etrat.ed by lamprophYl:es and subordinately by alka­line vein ro('ks affiliated to the alkaline Ditră, u Massif (sit.uatee! south-west of the study regiml).

1 n the Hogota-Tulgheş zone about 200 lall1-prophyres veins have been identified. The first description of the lamprophyres in t.he Tulgheş zone

(which is the object of an ample study) occurs in the geologic study of the Tulgheş zone (Atanasiu, 1929). Later an, the nonmetamorphosed vein rocks from the same zone were present.ed by Chelărescu (19:37 , 1938), Bercia, Sercia (1954) , Ionescu el. al. (1962), Arion et. al. (1963), Jakab (1981), Condurache et. al. (1985), Vodă, Vodă (1985) . The vein rocks identifiecl in wells in t hl' Hagot.a-Tulgheş zone were mentioned ar described by Mureşan, Mureşan (1989-1992), Mureşan (1993-1995), Airinei, Funkenhauser ( 1993), ancl Airinei (1994).

1. Petrography

Lamprophyres are, in general, microcrystalline, massive, of a grey OI' blackish , sometimes smoky colour, within which, in most. cases, melanocrat.e and leucocrate phellocrysts are visible. Very rarely, lam­prophyres contain large-sized (5-20 mm) mafic phe­nocryst.s, e.g. in Barat.ul Mare Valley. In case of thicker veins an incrl'asc of t.he grain size to their cent.ral zone has been notieed. No thermal cont.act phenomena (hornfelsizat.iolls) of t.he host rocks have been obsel'ved at the contact. with t.he lamprophyres.

8 L. IONESCU

2km

1- --

--_ .... Curmălura /

//

•

~ § 2

D 3

~ 4

~ 5 /

/ ""- 6 /'

----, "0 Hagota / I 7 / '-4.5-'

--1-- 8

.5 9 ------ -

Fig. j Sprcadiug; of the lamprophires in the Hagota-Tulghf'~ :l0" .. : 1. Harău Nappe (I-:lrct.ila (;rollp. 1' ... ' .. al1lbl'iall): L. Halaj

Nappe (Balaj Formation); 3, Pulna Nappe (Tulghc~ (;roup. C'alllbrian); 4. uvert.hrust.; S. Asod-RpZII Mal'c Digital io,,: (i.

predominant position of the veins 111 the lamprophyr" fields: Î, contol\\' lines nf thc lalllprnphyres frcquency (per .. e"t);

8, Valea PUlnei antiform : !:J. bOl'chol"s.

I

LAMPROPHYRES IN THE HAGOTA - TULGHEŞ ZONE 9

Table 1 Modal mineralogical composition of lamprophyres

Type of Family No. Major minerals Sporadic minerals lamprophyre Fp Amf Carb CI M.O. Vogesite Syenite 1 16 18 6 10 Fk=34 Serp=16 Spessart.ite Diorite 12 18-52 0-38 0-40 0-38 2-28 Serp=O-lO Q=0-10 Bi=0-7 I\ en;ant.ite Diorite 1 22 8 6 Bi=18 Malchit.e Diorite 1 18 29 22 5 Q=18 Odinite Gabbro 4 16-66 8-42 8-35 10-22 Bi=8( 1probă) Beel'bachite Gabbro 2 50-54 0-6 2-11 36 Py=8-18 ? 1 44 18 18 Ab=30 Q=6 Camptonite? Alk. gab. 1 34 18 16 8 Bi=lO Py=12 01=3

Legend:No-nllmber of analysed samples; Fp-plagioclase feldspars; Amf-amphiboles; Carb-carbonates; Cl-chlorite;

M.O.-opaqlle minerals; Fk-potash feldspar; Serp- serpentinic minerals; Q-qllartz; Bi-biotite; Py-pyroxenes; Al-albite ;

Ol-olivine.

In general , the veins are steeply dipping and are grouped into fields within which the veins display a relatively constant spatial position.

Almost alilamprophyres are affected by carbonata­tiOllS (mostly calcitizations); calci te occurs as veins, masses 01' impregna.t.ions in the rock mass. Mureşan (Hl91) considered that the pink carbonate veinlets are genet.ically relat.eel 1.0 the Ditrău alkaline massif.

Lall1prophyres are of ten pyritized. Pyrite occurs, in general, as idiomorphic grains, disseminated in t.he rock anei locally concentrated on fissures. The pyriti­zat.ions and limonitizat.ions of the lamprophyres can be spread on a restricteel distance in the adjacent. rock. In very many cases, lamprophyres are intensely altered, appearing as a friable aggregate formed of carbonates, limol1ite, chlorite and serpentinic miner­als.

In some cases, one coulel observe that lamprophyres include angular fragments of epimetamorphic rocks belonging t.o the Tulghe~ Group and in one case, in the Sumuleu Valley, a fragment of pink syenite, sim­ilar t.o those known in the Ditrău alkaline massif.

The majority of stuclied lamprophyres from t.he Hagota-Tulgheş zone belong to the diorite family, being of spessartite type and one kersantite sample and one malchite sample, and subordinately to the gabbro family. of the odinite, beerbachite, possibly cam ptonit.e type (from the alkali gabbro family). One lamprophyre rich in potash feldspar was assigned to the vegesites. that belong to the syenite family. The mod al mineralogica.l composition of the lamprophyres st.udied undeI' t.he microscope is presented in Table 1.

1.1 Vogesite

The rock consists of long prismatic amphibole phenocrysl.s, partly chloritized and opacit.ized. in-

c1uded in a feldspathic-carbonatic mass, locally serpentinized. Other melanocrate phenocrysts, entirely substituted by carbonates, chlorite and limonite,could represent pyroxenes. These rocks in­clude large nests, visible macroscopically, formed of carbonatic xenomorphic grains.

The groundmass consists of smalt. xenomorphic grains of perthi tic potash feldspar , of ten forming au­reoles arounel the carbonat.ic nests. Besiele them fine carbonatic masses, serpent.inic minerals anei mag­netite are notieed.

In 1929 Atanasiu deseribed, in the Tulgheş zone, a lamprophyre, possibly a vogesite, formed of amphi­bole (entirely altered), in association with felelspar (orthose ?). The phenocrysts are chlori tizeel 01' su b­stituted by calci te.

1.2 Spessartite

The matrix of these rocks consists of intermediary plagioclase felelspars and amphiboles, besiele reduced amounts of biotite , potash feldspar , quartz, olivine anei magnetite. When present, the phenocrysts are representeel by amphiboles anei plagioclase feldspars ; these minerals are elecomposed, being replaced by carbonates, serpentinic minerals , opaque minerals and limoni te.

The groundmass is generally altered. Thus, the plagioclase feldspars occur as rods and polysynthet­ieally twinned prisms, replaced partially by caleite, sericite and sel'pentine; in places, they are saussuri­tized. Potash feldspar (orthose) is found sporadically, being partially 01' totally altered into sericite. The presence of sodium feldspar, as xenomorphic grains, points to albilization phenomena. Amphiboles are found as prisms and rods, partially or totally opacit­ized, replaced by chlorite and epidote. Biotite scales and lamellas are corroded anei ranelomly spread in the

10

rock mass. Oii vine is tot.ally replaced by serpent.inic minerals. The opaqup minerals are represented by magnetite. locally replaced by hemat.ite OI' complet.ely Ipached. Caleit.e is almost. omnipresent, frequently occurring in very large amounts; it replaces the phe­nocrysts 01' invacles the rock mass. Quartz is locally observed as veinlets 01' nests formecl of xenomorphic, angular grains, wit.h normal to weakly undulatory ex­tinction.

In 1929 At.anasiu iclentified a spessartite in the Tulgheş zone. The described rock is of a greenish colour, with a silky lust.er, a l'lIsty alteration crust, alld slightly schistous. U neiel' the microscope, one can observe a netwol'k of elongated crystals of twinned fpldspars. Interfingereel with short. amphibole prisms. Oligoclase-anclesine is altereel into caleite anei epi­dot.e , and t.he brown hornblenele into chlorit.e anei epidot.e. The meshes of the network are filleel with chlol'it.e, epielote anei caleite. the primary minerals being unrecognizable. Another spessartite displays largp-sizecl fpldspar phenocrysts anei the amphibole phenocrysts are ent.il'ely altereel.

Tlw spessart.it.ps deseribeel by Ionescu et. al. (19(:)L) in t.he Tulgheş-Corbu zone display a panidiomorphous-granulated st.ructure, being formeel of a network of elongated cl'ystals of twinned felelspars intercalateel with brown amphiboles , as idiomorphic prisms. ChIOl·it.e , epidot.e and caleite occur in the meshps of t.he net.work. Felelspar develops as pris­matir. crystals of maximum 0.5 mm long and it. is often caleit.ized and epidotized. Amphibolite is, gen­erally. altered into chlorite anei epidote. Opaque min­erals are aboullding (5% of the rock mass).

1.3 Kersantite

I\ersantites are rocks of a blackish colour and COIl­tain relict. phenocrysts which, according t.o the hexag­onal cont.our, seem t.o have been a biotite replaced by seconelary minerals (carbonat.es, chlorite). Other in­t.ensely serpentinized and carbonatateel minerals. ini­t.ially probably an olivine, are very rarely found .

The groundmass consists of idiomorphic lamellas of biotite , short. prisms of amphiboles, wit,h interca­lat.ions of xenomorphic grains of int.ermediary plagio­clase feldspars anei possi bly of albite . The rock also cont.ains opaque minerals (magnetite?) and is pene­t.ra.t.ed by t.hin carbonatic veinlets.

1.4 Malchite

Reliel. phenocrysts of quartz and caleitized felelspars are observed uneler the microscope. The grounclma.<;s is altered , the prismatic amphiboles be­ing opaci l.ized anei replaceel by chlorite. The ma­tl'ix indudes short. lamellas of chlorite, xenomorphic

1. IONESCU

grains of caleite, cubic OI' xenomorphic cryst.als of opaque minerals. fine grains of quart.z . Carbonat.ic banels are crossing t.he rock mass.

1.5 Odinite

These rocks are intensely altereel , being invadeel by carbonates, chlorite and limollite. The phenocryst.s, after cOlltours initially pyroxenes , feldspars and am­phiboles. are totally replaceel by seconelary milH'rals. 1 n one section, plagioclase felelspar is fresher , gpner­ally being replaceel by carbonatps anei sericitp. Th€' mafic phenocryst.s are entirely substituteel by chlorite and carbonates. Xenomorphic relicts of biotite occur 111 one ca.<;e.

The primary minerals of the grounelma.<;s are re­placeel by carbonates , chlorite anei limoniie. The opaque minera.ls are founel as square or skeletic forms (ilmenitc?). Carbonates invad€' the rock ma.,>s 01' oc­cur a.,> veinlets.

The lamprophyre veins, possibly oelinit,es , de­scribeel by Atana..,iu (1929) in the Tulgheş zone, have a greenish colour and a rusty alterat.ion crust.. They elisplay a massive texture anei a holorrystaIline­porphyric structure. The phenocrysts are repre­sented by oligoclase-andesine. The matrix consists of felclspar anei altered amphibole crystals. that. forl1l a network whose meshes are filled with chlol'ite.

1.6 Beerbachite

The mafic mil1erals of these quasi-echigranular I'Ocks are represent.ed by partly chloritized pyrox­enes (augit.e), anei t.he salic ones by carbonatateel and sericit.izeel plagioclase felelspars. The l11aill opaque mineral is represent.eel by pyrite , founel as limonitized cu bie crystals OI' as xenomorphic aggregates . As sec­ondal'Y minerals, carbonat.es are found in l'elatively small amounts , besiele cla.yey minel'als aneI limonit.e.

1. 7 Camptonite

An identifieel lamprophyre, possibly a camptollit.e. consist.s of cryst.als of felelspars, amphiboles. pyrox­enes and olivine, strongly altereel anei invaeleel by S('('­

onelal'Y minerals. The campt.onites elescribeel by At.anasiu (1929) in

the Tulgheş zone are rocks with a basaltic aspect. They elisplay a massive text lire anei a holocrystaIline­porphyritic structure. The phenocrysts are repl'e­seuteel by titanaugite (partia.lly 01' totally substi­tuteel by chlorite anei caleite), barkevikite, and locally olivine (altereel iuto antigorite anei ca.Iciie) 01' quartz (a.<; ma.'>Ses surrouneleel by a pink rim formed of fine roels of iron oxieles ?) . The microcryst.alline matl'ix is constituteel of barkevikite, pyroxene, opaque minerals (abouneling), calcit.e and small amounts of feldspar,

r. LHPROPHYRES IN THE HAGOTA - TULGHEŞ ZONE 11

analcime and apatite. The author considered that these rocks differ [rom the normal camptonites by the absence of biotite and the presence. only sporadical, of feldspar.

These rocks, described by Ionescu et. al. (1962) in t.he Tulgheş-Corbu zone, display a massive text.ure anei a holocrystalline structure. The oii vine anei py­roxene phenocrysts occur in a microcrystalline mass, formed of augit.e. barkevikite, plagioclase, zoisite, opaque minerals,sphelle and apatite. Quartz occurs sporadirally as whit.e-greenish 3-4 mm thick masses. surroundeel by a pinkish rim formed of fine roels of iron oxide::i.

Campt.onites presented by Arion et al. (1963) con­tain phenocryst.s of pyroxenes. olivine and, locally, barkevikit.e, included in a microcrystalline matrix, constit.uted of augit.e, plagioclase, barkevikite, and opaque minerals.

1.8 MOllchiquite

Monchiquites elescribed by Atanasiu (1929) in the Tulghpş zone are compact, basaltic-Iike rocks, of a grey-blackish colour. They display an alteration crust of a rusty colour. In places, fine pyrite grains and calcite spherules are observed with the naked eye. Monchiquit.es show a Illassive texture and a hypocrys­talline porphyric st.ructure. The phenocrysts of augite (alt.ered into chlorit.e. calci te and sphene), olivine (alt.ereel into serpentine and calcite), locally barkevikite, basic plagioclase feldspar and biot.ite are incluc\ed in a l1lat.rix formeel of barkevikite, opaque minerals, analcime, anei sporaelically glass, sphene anei apatite. It is to not.e the absence or reduceel presence of biotite and the prevalence of augite anei olivine.

Atanasiu (1929) assigneel t.o the camptonite anei monehiquite series some strongly altered lampro­phyres, of a green 01' grey-greenish colour, with a crypt.ocryst-alline-porphyric structure. The phenoele­ment.s, locally large-sizeel (more than 1 cm), are to­tally alt.ereel, being replaced by chlorite (formeI' py­roxenes?) 01' serpent.ine (at. the expense of olivine ?). Remains of unaltereel biotite are founel very rarely. The cryptocrystalline mat.rix is invaded by calci te, t.he primary minerals being completely altered.

CheIă.re::ieu (1937) describeel several monchiquites, intensely altered hyelrothermally (frequently propyli­tizeel), which occur besiele the polymetallic sulphides in the Tulgheş zone. The primary phenocrysts are, at present, substituteel: feldspar by calcite, sericite and quartz, augite by pennine, and olivine (or analcime) by serpentine, calcite. quartz anei iron oxides. The

groundmass is a mixture of calci te, iron oxieles and, more seldom, antigorite, pennine and zoisite.

Ionescu et al. (1962) described monchiquite in t.he Tulgheş-Corbu zone. These rocks are of a dark grey colour and display a hypocrystalline-prophyric struc­ture, with a basaltic aspect. The augite and oii vine phenocrysts are included in a microcrystalline mass, constituted of augite, barkevikite, opaque minerals (ilmenite, pyrite), sphene and apat.ite. The pyrox­ene phenocrysts occur as short prisms. up to 2-3 m long, twinned, with clinochlore ami calci te on fissures. Oii vine is almost completely transformed into serpen­tine and calci te.

Monchiquites describecl by Arion el. al. (j 963) contain rare phenocrysts of oii vine and pyroxene in­cluded in a hypocrystalline matrix of barkevikite. pyroxene and opaque minerals. In places pyrite is abounding.

1.9 Othel' lampl'ophyres

They are rocks hard to define eit-her due to the advanced mineralogical alt.erations 01' to the impos­sibilit.y to assign them to the accepted petrographic classifications.

Thus. a lamprophyre cont.ains, beside plagioclases, a large amount of albite (about 30%), both feldspars being easily sericitized. The chlorite scales preserve the long-prismatic contour of some formeI' mafie min­erals, possibly pyroxenes.

A lamprophyre with enclaves of crystalline schists has been sampled from the ppak between t.he Balaj and Baratul Mare valleys. The lamprophyre mass includes: very large (up to 1 cm), t.abular-prismat.ic phenocrysts, completely serpentinizeel and part.ially calcitized, probably initially pyroxene; t.he minerals with a hexagonal contour, entirely serpentinized and carbonatatecl, probably representing formeI' amphi. boles; very large grains, serpentinized, with rows of opaque minerals on fissUl'es. formecl at the expense of pre-existent olivine. AII these st,rongly altereel phenocrysts are included in a grollnclmass formecl of clayey minerals, carbonates, serpentinic minerals. The rock is penetrat.ed by calci te veinlels. The en­closeei angular elements represent up to 40% of the rock and are formed of quartzites. qllartz-sericite schist.s and quartz-graphite schists.

Mureşan (1991, 1994, 1995) describeel schists en­claves in lamprophyres, in the wells 8-Barat.lIl l'vlic (here, the lamprophyre ha.., a fluidal texture), 1-Hagota (calci te epigenet.ic crosses the lamprophYl'e and quartz schist.), 47-Putna. 7-Beche, 21-Putna, 43-Baratul Mare. In the well 43-Baratul Mare, MUl'eşan (1995) identified a highly alterecl lamprophyre that contains an enclave in an older lamprophyre.

I

12 L. IONESCU

Table 2 Average contents in minor elements (in p.p.m.) of the lamprophyres grouped according

to their spatial position (azimuth of the dipping sense)

Pasitian Na. Ag As B Ca CI' Cu Mn Ma Ni Pb Sn Zn 340-20u 11 0.03 O 10 34 104 53 289 2.2 156 29.8 1.1 220 80-11.')° 10 0.03 20 27 35 76 59 391 2.1 149 18.3 1.0 28.5 210-230° 5 0.08 20 O 41 130 70 150 2.6 160 32.0 0.8 128 260-280° 5 0.20 40 36 40 79 36 224 2.0 132 21.6 1.0 110 300-320° 7 0.04 29 33 20 82 40 80 1.4 93 19.7 0.6 44

No. = number of analyses

1.10 Other vein rocks

In t.he Hagota-Tulgheş zone, other vein rock types have been deseribed, some of them ofthe diabase t.ype and others, more numerous , affiliated to the Ditrău massif.

1.10.1 Diabases

A tanasi u (1929) consielerf'd that in the Tulgheş wnc diabases occur beside melaphyres as intercala­tions int.erbedded in t.he Mesozoic sedimentary de­posit.s overlying the crystalline.

('helărcscu (1937) describeel veins of porpylitizeel diabases beside t.he epigenetic mineralisations in the Asoel Brook zone. Diabases consist of felelspar, olivine, augite, antigorite, pennine, sericite, calcit.e, anei quartz. Oii vine, the olelest mineral, is found as idiolllorphic erystals, locally substituted by antig­Ol'ite, calci te and quartz. Felelspar is altereel in the interior , with neoformation of sericite and saussurite. Augite is altered into brown hornblende towards the periphery.

Ionescu et al. (1962) mentioned the presence of t.he diabases in the Tulgheş-Corbu zone, in the north­east.ern part of the Barasă.u Valley basin. These dia­bases are described in general; t.hey have a grey colour with greenish hues, an ophiolitic structure and a mas­sive t.exture.

Arion et. al. (1963) elescribeel four diabase veins, of less than 1m t.hick, unconformable versus the epimetamorphic erystalline schists from the right. sicle of the PULna Valley, in the zone of the Hagota villagf' . These rocks display a grey colour and a ma.ssive aspect.. They have and intersertal structure , within which prislllatic-acicular erystals of basic plagioclase felclspar include crypto-crystalline or glass)' masses , probably of pyroxenic origin. These masses are strongly altereel anei calcitized. Partly altel'f'(l lamellas of biot.ite, as well as granular clus­ters of opaquf' minerals beside secondary minerals are

also frequently observed. Mureşan & Mureşan (1990, 1(91) ielentified dia­

bases in t.he wells 3-Putna anei 1-Hagota. Thus, the diabase int.ercept.ed in the well 3-Putna, in the inter­val 1042-1045m, consists of felelspars, pyroxenes and amphiboles. The melanocrates are rhloritizeel. In the well 1-Hagot.a tlll'ee eliabase veins are describeel in the int.ervals 629-6311ll, 828-833m and 968-970m. The first eliabase is altereel anei displays an ophitic struct.ure. Hypicliomorphic ff'lelspars, partly serici­t.izecl anei calcitized, can be noticed , wit.hin whirh all1ph iboles partly altered into biotitf' are developi'c1. The second vein has a eliabase strucutre due to the hypieliomol'phir plagioclase felelspa.rs , wit.h different t.rendings, bet.ween which oparitizf'dand chloritized melanocrates are clevelopp.eI. The third diabase shows a similar structurI". Feldspars are saussuritized anei partly calcitized, anei melanocrates are opacitizecl anei chlorit.izeel.

1.10.2 Alkalille vein rocks

These rocks, associat.ecl OI' not with mineralisa­t.ions, wel'e ielentifiecl in boreholes by ivIureşan (1989-1995) anei Funkenhauser, Airinei (1992 , 1993). Thus, Mureşan elescribeel: a. syenit.ic rock with monazite, relateel t.o the meta.lIogenesis of the Dit.rău massif. in the well 5-Ha.gota; two veins of calcitized t.inguait.es, in the well 29-Baratul Mare; a massive, fine-graillf'el vein rock (with an enclave of a pyritous, probably syngenetic, metamorphosecl mineralisation) , t.hat is also founel upwards in the borehole column as an en­c1avf' indudecl in a lampl'ophyre , in the well 22-Put.na.

Fukenhausel', Airinei (1992, 199:3) described: syen­it.es a.nclmicrosyenit.es in the wells 5-Put.na, 22-Putna anei 43-Baratul Mare; an intrusive. more aciel rock, with a porphyric st.ructure. beside lamprophyres , in the well 24-Balaj; liebneritic syenites in the well 7-Beche.

2. Geochemical consideratiollS

92 out. of the 200 lamprophyres ielent.ified in t.he Hagota-Tulgheş zone have spect.rally bf'en analysf'd

LAMPROPHYRES IN THE HAGOTA - TULGHEŞ ZONE

for 1(3 elements. It it to note that, Bi, Cd, Sb and W are llslIally below t.he detect.ion limit.

The data presented in the above table do not. indi­eatp any law of any preferential geochel11ical compo­nellt of the lampl'Ophyres grollped according to their spatial posi t ion (azil11l1th of the dipping sense), l'e­gardless of the sampling site.

Table a present.s the average content.s (in p.p.m.) of the lamprophYl'es gl'ouped according to their geographic spreading (Fig. 1), in certain fields, present,ed from north to south, regardless of t.he vein position.

nes, according to the chemistry of the rocks: the camptonite-monchiquit.e series , representing elif­ferentiation product.s of the alkaline magmas, of Atlantic type; the vogesite-spessartine-odinit.e anei diabase melaphYl'e series , representing differentiaiioll product.s of t.he alkali-calcic , granito-dioritic anei gabbro-peridotitic l11agmas, of Pacific type. Table 4 presents the results of the chemical analyses (major elements) effectuaied by Atana.'liu (1929) on some lamprophyres from the TlIlghe§ zOlle. They have been defined on the basis of the petro­graphir analyses. In sample 2, anei possibly samples :)

Table 3 Average contents of the minor elemellts (in p.p.m.) of the lamprophyres grouped

according to their geographic spreading

Zone No. Ag As B Ca CI' Cu Mn Ma Ni Pb Sn Zn A.sod 6 0.03 O 41.7 .50 91 76 191 4.1G 1:38 ;p ') 1.16 157 Hezu Mare 17 0.02 O 21.4 29 62 42 .55 1 2.17 6') )~ 13 .. 5 0.58 248 Pllt.na-B.M. 22 0.07 18 6.4 n 139 76 296 3.72 184 30.1 0.86 99 B.M. llpst.realJl 15 0.06 20 27.0 35 132 G9 167 2.93 214 21.2 1.00 170 SlllJluleu 23 0.03 17 9.6 26 81 57 309 2.93 130 31.4 1.65 166

No. = number of analyscs, B.M. = BaraLlIl Mare

Table 4 COlltents of major elements of some lamprophyres in the Tulghe§ zone (Atanasiu, 1929)

Oxydes (%) 1 2 3 4 5 6 7 Si02 37.24 34.7:2 38.78 39.10 33.74 26.48 'J5.81 Ti02 3.40 3.02 5.10 4.01:5 2.86 1.61 2.78 Ah03 U.62 9.82 11.64 13.84 14.12 15.72 19.02 Fe2 0 ., 2.47 3.24 4.22 ,s.41 4.78 3.77 1.44 FeO 13.37 11.39 12.30 8.39 9.84 11.28 8.72 MnO 0.86 l..56 0.8,5 0.90 0.60 1.51 0.93 1'vlgO 6.59 8.43 8.24 9.11 13.23 10.14 6.76 CaC) 13.96 10.92 D.24 8.88 6.00 9.67 5.52 BaC)+SrO 0.09 t.races 0.19 tl'aces nel!. ndt ndt. Na2 0 2.04 2.47 0.93 3.93 5.15 3.10 2.90 1\ 20 1.29 0.6,s 0.10 nclt nclt. 0.55 168 P 2O ,5 0.13 t!'aces 0.11 0.76 0.16 O . .,~

.~ I ndt SOs 1.44 0.84 0.G7 1.40 3.64 0.49 ndt. I-bO 0.40 2.06 0.G2 0.34 0.49 0.77 0.2,5 CO2 +H20+ 4.97 11.04 6.78 4.6,1 6.34 13.73 "1.80

TOTAL 100.87 100.16 99.77 100.7,~ 100.95 99.09 100.6.5

1, camptonite. Piat:ra Ro~ie Românească; 2, monchiquit.e, Magyaros; 3, monchiquil'.e, Fuges; 4, call1pt,onite-monchiquit.e.

Baratul J\.lic; 5, camptonite-monchiquite, Putna Brook; G. campt.onite-monchiquite, PlItna Brook; Î. spcssartille, Stejii Mnunt.

(·losses=3.04 %): ndt.=lIndetel'lninccl .

The resulting values do not indicate any law concern­ing t.he variat-ion of the contents of the analyseel ele­ments arcording t.o t.heir regional spreading.

At.anasiu (1929) grouped the lamprophyres anei diabases in the Tulgheş zone into two rock se-

anei 6 , t.he apparent. lower rontents in SiO~ have been regareled at the expense of some high contents in CO 2

anei H2 . Because of the smallnumber of analyses, it is elifficult. to characLerize and elefine t.he lamprophyre types from t.he chemical point. of view .

..

14 L. IONESCU

O·

Fig. 2 - Oiagram of the lamprophyre veins positions (azimllth of the dipping sense) in the Hagota-TlIlgheş zone (per cent).

TllP dat.a presented in tables 2, 3 and 4 point out (hat in t.he Hagota-Tulgheş zone the contents of lam­prophyres in the analysed elements do not depend :;ignificantly either 011 tlH' spatial position or on the geogri-lphic spreading of these rocks. AII this suggests the commoll origin of ali lamprophyres in the study ZOIlf'.

3. Spreadiug and positiou of lamprophyres

In t.he llagota-Tulgheş zone lamprophyres are groupeel into severa! fie!ds (Fig. 1), situated in (Il!' Aso(l. Rezu Mare. Putna-Baratul Mare, Baratul 1\1(\]'(', F'iller-Şumuleu valleys zones. The lampro­phyre fielel:; occur mostly in tllP spreading area of the Tulgheş Group formations , showing a tendency to close a.t t.heir contact with the Balaj ancl Rarău na.ppes.

The spatial position of 98 out of 200 iclentified lamprophyres could be determined either directly,

with the compass, OI' indirectly , biogeophysirally (with t.he angular rod). The position of the lampro­phyres differ from one fielcl to another, being, how­ever, relatively constant within the same field (Fig. 1). With a few exceptions, the clipping of the lam­prophyres is sharp (60-90°). The diagram with the percentage representatioll of the lamprophyre posi­tions (azimuth of the clipping sense) has been clrawn up based on the 98 posit.ions measured (Fig. 2).

The above-lllentionecl cliagram inclicat.es that the majority of the lamprophyres are assignecl 1.0 a systelll of conjugated elirections, corresponeling to a syst.em of fractures wit,h a N-S t.rencl anei eastern elip:>, thal. is a fracture syst.em with an E-W t.renel anei N elips.

4. Dimensiolls aud volume (in perceutagc) of the lamprophyres

In the Hagota-Tulgheş zone, lamprophyres arf' quite frequently founel (Atanasiu, 1929). At the SUl'­

face, the thickness of the veins is in general submetric

I

LAMPROPHYRES IN THE HAGOTA - TULGHEŞ ZONE 15

(usually 20-50m), very selelom more than lm. Along t.lw strike. these rocks could be followed at the surface on limi teel distances (of metres order). The lampro­phyrf' bodies are usually unconformable versus the crysta.lline schists and quite rarely they occur as con­cordant veins.

AII the wells drilled in the Hagota-Tulghe§ zone int.ercepted lamprophyres. The thickness of the lam­prophyre veins in the drilling columns is, in general, of the metres order, even smaller. Apparently great thicknesses have been found in the wells: l-Hagota (13 m) , 21-Putna (19 m), 43-Baratul Mare (11 m), 47-Putna (11 m , 30 m, 11.5 m).

zone, the author considered that the genetic associ­ation of these rock is less probable. The mentioned lamprophyre series and the eliabase-melaphyre series, by their very similar chemistry, maele the mentioneel author to conclude that they represent products of the same magmatic phase, of Upper Triassic age.

Chelărescu (1937) considered the mineralizations in the Tulghe§ zone as post-metamorphic, associated with a hydrothermal activity related to the granodi­ori tic massifs anei lamprophyre veins. Later on, in 1953, he associated those mineralisations with the Neogene volcanic activity in the Călimani-Gurghiu­Harghita chain.

Table 5 Lamprophyres spreading in the wells in the Hagota-Tulghe§ zone

(according to Mure§an, 1989-1995; Ah'inei, 1993, 1994)

Well Loc. Depth No. Thickness % Well Loc. Depth No. Thickness % SI Hagot.a 994 13 42.0 4.23 S28 Bar. Mare 659 6 11.2 1.70 S3 Putna 1200 12 29.0 4.23 S29 Bar. Mal'e 645 1 3.5 0.54 S5 Putna 1410 10 17.7 1.26 S30 Asod 655 4 10.5 1.60 S6 Putna 1335 14 45.0 3.37 S42 Bar. Mare 700 2 2.0 0.29 S7 Beche 750 10 23.0 3.07 S43 Bar. Mare 550 10 29.4 5.35 S8 Bar. Mic 700 4 7.0 1.00 S44 Bar. Mare 720 1 5.0 0.69 S9 Bar. Mare 675 2 3.5 0.52 S45 Bar. Mare 602 2 7.5 1.25 SlO Balaj 650 6 20.0 3.08 S46 Bar. Mare 650 5 12.0 1.85 S19 Balaj 1165 6 21.5 1.85 S47 Put-na 400 11 79.2 19.80 S21 Put-na 476 4 26.0 5.46 S48 Putna 450 1 12.0 2.67 S22 Putna 662 15 43.3 6.54 S51 Putna 406 4 15.9 3.92 S24 Balaj 1114 6 18.0 1.62 S54 Putna 353 1 3.5 0.99

(Sd-well; Loc.=locations; Ad.=depth of t.he well; No.=number of lamprophyre veins intercepted; Thickness=total apparent

thicknesses; %-share of the lamprophyre int.ercalations in the lithologic column of the well; Bar.=Baratul)

Table 5 presents the systematic data on the spread­ing of the lamprophyres intercepted by wells drilled in the Hagota-Tulghe§ zone. Considering these data, it results that out ofthe 17,921mdrilled, 487.7m have been crossed by lamprophyres, totalizing about 150 veins, with an apparent average value of 3.25m. They represent about 2.72% of the rock investigated by drillings.

5. Age, genesis and relationships of lamprophyres with the epigenetic

mineralisatiolls

In the Tulghe§ zone, the alkaline character of the lamprophyres from the camptonite-monchiquite se­ries is assigned by Atanasiu (1929) to the affilia­tion of these rocks to the Ditrău alkaline massif, considered by the mentioned author of Upper Cre­taceous age at most. Camptonites and monchiq­uites should be younger, that is post-Aptian in age. Although the chemistry of the vogesite-spessartine­odinite and diabase-melaphyre series show affinities with the granodioritic intrusive massifs in the Tulghe§

Savul (1954) mentioned in the Corbu zone a close association between the lamprophyres anei mineral­isations, anei considereel that they originate in hy­elrothermal solutions elifferentiated at elepth, which representeel access ways of the fractures on which the lamprophyres are situateel.

In 1954, Bercia anei Bercia pointeel out that, for the mineralisations situateel north-east of Tulghe§, the absence of marcasite inelicates their formation at great elepths anei in reIat ion to the zones an which the lamprophyres were injecteel.

I\oczur (1973) mentioned that the mining works ca.rried out in the Şumuleu-Filler zone, proved that the mineralisations are closely related ta a lampro­phyre which presents, in the contact zone with the schists, pyrite anei chalcopyrite impregnations.

Anastasiu anei Constantinescu (1980) highlighted the association of the lamprophyres in the Jolotca zone with some mineralised veins.

In the Hagota-Tulghe§ zone there is a good spatial association of the lamprophyres with the epigenetic mineralisations (Şumuleu, Baratul Mare, Cibeni, Barasău, Sangeroasa).

t6

Nearby Tulgheş , although the density of the lam­prophyres is reduced, two of them are closely related to the epigenetic mineralisat.ions. Thus, the common sulphide mineralisation in quartz gangue, identified in the Cibeni Valley. occurs beside an intensely pyri­tized lamprophyre, both veins having a N-S trend. In (,111' Ohaba Peak zone one of the two weakly min­eralised veins with sphalerite-galena and lantanides ill carbonate-quartz gangue occurs, in the hanging \VaII , at a distance of ca 20 cm beside an intensely altered lamprophyre ,'anel displays the same position (260° /50°).

111 the Borsec-Tulghe§ zone, within the Tulgheş Group, there occur several vein lead-zinc minerali­sations related to lamprophyres. From this point of view, t.he sit,uation of the lamprophyres is, as fol­lows : lamprophyres are borelering on 01' they are in the vicinit,y of t.he mineralizeel veins, at Paltin , Sangeroasa, Obcina Mică , Baratul Mare; lampro­phyres occur as fragments in the mineralised brec­cias at Palt.in; lamprophyres are hosting the min­era lisations at. Palt.in , Pâraul cu Linia (Barasău) ,

Argintăria. This association was argued (J akab, 1981; Vodă, Vodă . 1985) by the fact that both lam­prophyres and the mineralised solutions used the same access ways.

As regards the age of the lamprophyres, we con­sider t.ha:t. they are younger than the epimetamorphics of t.he Tulgheş Group (Cambrian), younger than the overthrust.s in the area anei t.han the Asod-Rezu Mare digitation, younger t,han t.he Palt.in-type mineralisa­tions for which .Jakab , Popescu (1981) estimated a Cretaceous age, possibly Upper Jurassic, on the basis of t.he isot.opic age analyses, :105Pbp05Pb=0.17-0.18.

Received: Febru(I1'y 24, 1998

Accepted: October 80, 1998

1. IONESCU

References

Airinei, 1., Funkenhausel·. P. (1983) Report. Archives of "Geolex" S.A., M. Ciuc.

(1984) Report, Archives of "Geolex" S.A., M. Ciuc.

Anastasiu, N., Constantinescu, E. (1980) Reporl , A"chives of " Geolex" S.A., M. Ciuc.

Arian, M .. Ri~a. E., NedeJcu. V. (1983) Report , Archives of "Geolex" S.A .. M. Ciuc.

Atanasiu.l. (1929) Cercet.ări gcologice În Îtnp"ejlll'il11ile Tulghe~ului (judetul Neamt) An. Inst. Geo/. Rom., v. XIII, p. 165-371, Bucure~ti.

Bel'cia, E .. Bel'cia 1. (1954) Report . Archives of "Geolex" S.A .. M, Ciuc.

Chelăl'escu, A. (1937) Gisements metalliferes de Tulghe~. Ann. Se. Uni". Jassy, XXIII , II. p. 265-:J93. Ia~i .

Condurache. C .. Dudnic, G., Stl'ugaru, T. (1985) Re­port , Archives of "Geolex" S.A., M. Ciuc.

Funkenhauser, P., Airinei, 1. (1980) Report, Archives of "Geolex" S.A .. M . Ciuc.

Ionescu, C., Gheruci, O., Costache, P., Micu, C., Popa, Gh., Puiu, V., Puiu, M., Arian, M., Teucă, 1. (1962) Report, Archives of "Geolex" S.A., M. Ciuc.

Jakab. G. (1981) Contributii la cunoa~terea mineraliza­ţii lor plumbo - zincifere de la Valea Seacă - pîrîul Paltin (Carpatii Orient.ali) D.S. Inst. Geo/., LXVI/2 , p . 21-35. Bucure~ti.

- , Popescu, G. (1981) Date noi privind virsta ~i

geneza lIlineralizaţiilor hidrot.ermale din cristalinul seriei de Tulghe~ , zona Gheorgheni-Bilbor (Carpaţii Orientali). D.S. Inst. Geo/., LXVI/2 , p. 37-44, Bucureşti .

Mm'e§an, M., MUl'e§an, G. (1989) Report, Archives of "Geolex" S.A., M. Ciuc.

(1990) Report, Archives of "Geolex" S.A., M. Ciuc.

(1991) Report, Archives of "Geolex" S.A., M . Ciuc.

(1992) Report, Archives of "Geolex" S.A., M. Ciuc.

Mure~an. M., (1993) Report, Archives of "Geolex" S.A., M. Ciuc.

(1994) Report., Archives of "Geolex" S.A., M. Cîuc.

(1995) Report. Archives of "Geolex" S.A., M. Ciuc.

Vodă, Al., Vodă, D. (1985) "Considera~ii asupra unor lIlineralizatii epigenetice din zona crist.alino-lIlezozoică a "Carpaţilor Orientali" Stud. celT. geol.. geof., geogr .. Geologie, 30, p. 53-57, Bucure§ti.