Sibumasu Research Articles

Parallel Tethyan sutures in mainland Southeast Asia: New insights for Palaeo-Tethys closure and implications for the Indosinian orogeny

Two contrasting parallel tectonic sutures can be recognised through the Yunnan–Thailand region of mainland Southeast Asia; they are sutures of the Devonian–Triassic Palaeo-Tethys Ocean and a Permian back-arc basin. The Changning–Menglian and Inthanon suture zones are regarded as the Palaeo-Tethys Suture Zone. The Jinghong–Nan–Sra Kaeo suture is regarded as a closed back-arc basin. The Sukhothai Zone is no longer treated as a part of the Sibumasu Terrane, but is defined as the core part of the Permian island-arc system developed on the western margin of the Indochina Terrane. Two tectonic events are interpreted from the parallel sutures; a Late Permian collapse of the back-arc basin and a mid-Triassic collision of Sibumasu to the Sukhothai Arc of Indochina (= closure of the Palaeo-Tethys). The Early–early Middle Triassic thermotectonism of Vietnam as linked to the Indosinian orogeny by some authors is incompatible with the suggested timing of Sibumasu collision, but instead it is temporally closer to the back-arc compression of western Indochina.

Spatial gap between Lhasa and Qiangtang blocks inferred from Middle Jurassic to Cretaceous paleomagnetic data

We present paleomagnetic results from Middle Jurassic red sandstones of the Sangba Formation. Orientated samples were collected at 14 sites on north side of the Basu (30.1°N, 96.9°E), northeastern border of the Lhasa Block. After stepwise thermal demagnetization, high-temperature component with unblocking level of 680 °C is isolated from 7 sites. Primary nature of this magnetization is ascertained through positive fold and reversal tests at 95% confidence level. Combined with previously reported paleomagnetic results, tilt-corrected mean direction of D = 353.4°, I = 15.1°, α 95 = 14.1°, N = 8 is calculated, indicating that during Middle Jurassic the study area was located at 7.7°N ± 7.4°. Comparison with the Jurassic paleomagnetic data reported from eastern Tibet indicates that the Lhasa Block was located south of the Qiangtang Block at a latitudinal difference of 31 ± 11°. Compilation of paleomagnetic data further suggest that until the Cretaceous large spatial gap of more than 1200 km remained open between the Lhasa Block and the Qiangtang Block of eastern Himalayan syntaxis and eventually vanished during Tertiary. Cretaceous paleolatitude corresponding to this gap (13.0°N–31.0°N) is almost identical to that reported from Shan-Thai Block (25.4°N ± 5.2°). Furthermore, the Permo-Carboniferous sequences of Gondwanic affinity are distributed in western part of the Shan-Thai block as well as in the Lhasa and Qiangtang blocks. Keeping in view these similarities, we propose a new pre-collision (India vs. Asia) reconstruction model in which the Lhasa, Shan-Thai and Qiangtang blocks are shown in their respective order from south to north along southern margin of the Asian continent. The aftermath of gigantic India–Asia collision however introduced north–south compressional regime in the Asian Continent that eventually played a role in eastward extrusion of the Shan-Thai Block from an area between the Qiangtang and Lhasa blocks.

Internal deformation of the Shan-Thai block inferred from paleomagnetism of Jurassic sedimentary rocks in Northern Thailand

Paleomagnetic samples of red sandstones were collected at 16 sites from the Lower to Upper Jurassic Phu Kradung formation and the Upper Jurassic Phra Wihan formation around Nan City (19.2°N, 101.0°E) in the southern region of the Shan-Thai block. After stepwise thermal demagnetization, a high-temperature component with an unblocking temperature of about 680 °C is isolated from 11 sites. We interpret this to be a prefold characteristic remanent magnetization because of a positive fold test at the 95% confidence level. The tilt-corrected mean paleomagnetic direction from 11 sites is D = 32.3°, I = 33.3°, α 95 = 12.2°, k = 15.0, which gives a paleomagnetic pole for this area of 60.1°N, 186.5°E with A 95 = 11.7°. Compared with a Jurassic paleopole for the stable part of the Yangtze block, we observe a clockwise tectonic rotation of 12.8°, which is similar to the observed rotation (18–28°) of the northern region of the Shan-Thai block. This amount contrasts with a large rotation of more than 45° that is estimated from the narrow zone extending from Luxi to Mengla in the central region of this block. This declination aspect suggests that a coherent whole block rotation by about 20° of the Shan-Thai block took place in an earlier phase during indentation of India into Asia and that an internal deformation with additional local rotation between 25° and 77° followed within a limited zone in the central part. The internal deformation of the Shan-Thai block absorbed the stress on the Asian continent induced by indentation of India as well as its coherent whole block motions of clockwise rotation and southward displacement.

The welding of Shan-Thai

The Shan-Thai Terrane is viewed as a remnant of paleo-Tethys in South East Asia. The more internal “Thai” elements of Shan-Thai, bordering with Indochina, are of Cathaysian type, while the more central part of the terrane is of transitional “Sibumasu” character: The external “Shan” elements of Shan-Thai that left Gondwana last have a clear cold-water imprint. Petrological and paleontological evidence corroborates the end Triassic—earliest Jurassic Late Indosinian orogeny, as the main Paleotethyan tectonic closure event. Its main axis consists of the Mae-Sariang Zone, which can be followed over Mae Sot to Kanchanaburi and Chanthaburi, from where it extends into southern Thailand and Peninsular Malaysia. Cenozoic Himalayan escape tectonics, alternating strike-slip movements and rotation severely compressed Shan-Thai, opened the Gulf of Thailand, disrupted the original alignment of the Mae Sariang zone and Gondwana-Tethys divide, and shaped the present tectonic configuration of SE Asia.

New micropalaeontological evidence for a Late Triassic Shan-Thai orogeny

The Shan-Thai block is viewed as a remnant of Paleotethys in South East Asia. The general consensus about its origin is that it happened through the rifting from Gondwanaland and final amalgamation to Eurasia, sealed by fluvial-shallow marine Jurassic deposits. As the main Paleotethyan closure, the Nan-Uttaradit/Nan-Chantaburi and Bentong-Raub sutures were proposed by other workers. However, a suture further west, flanked by the Gondwana-Tethys divide (GTD), is advocated here as the main Paleotethyan closure. The Middle and Late Triassic radiolarian faunas were extracted from a chert-sequence in the Mae-Sot and Umphang areas of NW Thailand. The radiolarian faunas indicate early Ladinian, early-middle Norian, and Norian-Rhaetian, individually. The Triassic chert-sequence is overlain by the ‘Jurassic base-conglomerate’. The limestone and chert clasts in the conglomerate yield Early-Late Triassic conodonts and Middle-Late Triassic radiolarians, respectively. Chert clasts in the conglomerate yield among others Norian-Rhaetian radiolarians that are correlative with those from TM3, while Early-Late Triassic conodonts are found in limestone clasts. The silici-pelagic origin of the clasts suggests the Mae Sariang Zone that amalgamated the parts of the Shan-Thai block. This first finding of Late Triassic radiolarians from chert-sequence, next to the Middle Triassic and older radiolarian faunas, adds another element to the reconstruction of the sequence now comprised in the Mae Sariang Zone, west of the Nan-Uttaradit Suture. The occurrence of Triassic limestone, as that of the Chaiburi Formation in the Mae Sariang Zone, or the Kodiang Limestone in the “Western Zone”, may elucidate the question about the provenance of the Triassic conodont-bearing limestone clasts in the Jurassic base-conglomerate that seals the Mae-Sariang Zone. The newly dated Triassic sequence is further sealed by the continental-shelf deposits of the Toarcian-early Bajocian Hua Fai Group.

Faunal affinity of Toarcian-Aalenian (Early Jurassic) bivalves from Mae Sot and Umphang (Tak Province), Northwestern Thailand

In the Mae Sot and Umphang areas (NW Thailand), Jurassic strata seal the Permian and Triassic substratum of the Shan-Thai terrane with a brecciated conglomerate. Pliensbachian to Early Bajocian shallow marine strata are intercalated within the partly terrestrial Jurassic sequence. Thirty-five Toarcian-Aalenian bivalve species from Mae Sot and Umphang were identified. Among these,Eomiodon chumphonensis Hayami is known only from Thailand, whereasParvamussium donaiense (Mansuy),Myophoriella saurini Hayami,Thracia loducensis Hayami,Pholadomya (Bucardiomya) fontainei Hayami,Thracia loducensis Hayami andModiolus sestiniae Hayami were originally described in Vietnam.M. sestiniae also occurs in Iran. The greater part of the fauna, however, shows varying degrees of affinity with Myanmar (6 species), Cutch (10 species), Japan (13 species) and Europe (9 species), Levant (2 species). In view of these, it appears that these highly endemic Toarcian-Aalenian bivalves from Thailand characterize the Southeastern Asian Province of Tethys.

Triassic foraminifers of the Lampang Group (Northern Thailand)

Triassic foraminifers are recognized, for the first time, in limestones from four localities of the Lampang Group (Northern Thailand), tectonically assigned to the Sukhothai Subterrane (Sukhothai Folded Belt) which is located between western the Sibumasu (Shan-Thai) Terrane and eastern Indochina. Four foraminiferal associations are distinguished: (1) Glomospirella lampangensis, n. sp., (2) Pilammina densa, (3) endothyroid foraminifers- Diplotremina astrofimbriata, and (4) Aulotortus sinuosus microfaunas. Based on comparison with the coeval European faunas, they are thought to be (1) Early Triassic (?), (2) Anisian, (3) Ladinian (?), and (4) Carnian in age. Important taxa of these associations are common to those of South China and Southeast Asia. Most of them are closely similar to those of Europe, and show a remarkable contrast with those of Middle and Late Permian foraminiferal assemblages having many provincial and endemic characters. Glomospirella lampangensis, n. sp. is herein systematically described among the distinguished 41 species.

Permian and Triassic Radiolaria from Northwest Thailand: paleogeographical implications

Well-preserved radiolarians were recovered from seven sections in the Mae Hong Son-Mae Sariang area, northwestern Thailand. 51 species assigned to 34 genera are identified, including 1 new species ( Triassospongosphaera erici Feng sp. nov.) and 19 unidentified species. They are divided into the Late Permian, late Ladinian and middle Carnian radiolarian assemblages. Newly identified radiolarian assemblages, together with the published radiolarian biostratigraphic data from this region, indicate that there was a pelagic basin during the Late Paleozoic and Triassic. This basin was joined to the Chiang Dao and Changning-Menglian oceanic basins, and they represent the main oceanic basin of the Paleotethyan Archipelago Ocean. This main oceanic basin was situated in the traditional “Shan-Thai Block”. Therefore, “the Shan-Thai Block” was not a single block during that stage, but composed of the Paleotethyan Ocean and two continental terranes that were affiliated with the Gondwana and Cathaysian domains, respectively.

Discovery of plate‐type scyphocrinoid loboliths in the uppermost Pr̆ídolían–lowermost Lochkovian Upper Setul limestone of Peninsular Malaysia

AbstractScyphocrinoid loboliths, the bulbous floats attached to the roots of a group of large Late Silurian to Early Devonian crinoids, were found within the top part of the Upper Setul limestone at two localities, in a band of limestone at Memplam Bay and in limestone blocks from a soil quarry at Guar Jentik, in northwest Peninsular Malaysia. The loboliths belong to the plate type, characterized by having plated chamber walls, few internal chambers and the presence of chamber openings near the axil of each primary root. Plate loboliths belong to species of Marhoumacrinus and Camarocrinus of the uppermost Pr̆ídolían to lowermost Lochkovian, and occur generally above cirrus loboliths, which are Pr̆ídolían only. Armoured floats are believed to have provided better protection against predators and the physical elements. These loboliths are important for correlation with other occurrences worldwide and especially within the Shan‐Thai or SIBUMASU (SinoBurMalayaSumatra) terrane of southeast Asia. Copyright © 2005 John Wiley & Sons, Ltd.

First dinosaur from the Shan–Thai Block of SE Asia: a Jurassic sauropod from the southern peninsula of Thailand

A vertebra collected from the Jurassic non-marine Khlong Min Formation of southern Thailand is referred to the family Euhelopodidae, a group of sauropod dinosaurs that apparently was endemic to eastern Asia during the Jurassic and Early Cretaceous, at a time when that part of the world was isolated from other land masses. The occurrence of a euhelopodid in the Jurassic of the Shan–Thai Block supports the idea of a collision of the Shan–Thai Block with the Indochina Block, thus establishing connections with ‘mainland Asia’, early in the Mesozoic, probably before the Jurassic.

Correlation of Triassic stratigraphy between the Simao and Lampang-Phrae Basins: implications for the tectonopaleogeography of Southeast Asia

Based on our extensive fieldwork in southwestern Yunnan and northern Thailand, followed by detailed stratigraphic and paleontological studies, we propose that the Triassic Simao Basin in Yunnan can be correlated with the Triassic Lampang–Phrae Basin in Thailand. Strata equivalent to those in the southern Lancangjiang sub-basin have not been identified in northern Thailand. We consider that during the Triassic the Simao and the Lampang–Phrae Basins belonged to the same tectonopaleogeographic unit. The orogenic belt to the east of this unit includes the Nan–Uttaradit and Ailaoshan sutures. The ‘Shan–Thai Block’ in northern Thailand, can be divided from east to west into the Sukhothai, the Inthanon, and the Shan terranes. According to tectonopaleogeographic correlation, our results support the idea that the Sukhothai Terrane, including the Lampang–Phrae Basin, belongs to the Cathaysian domain and not to Gondwana domain, and that the geosuture corresponding to the Changning–Menglian Suture in Yunnan must lie to the west of the Sukhothai Terrane in Thailand.

The Devonian–Lower Carboniferous succession in Northwest Peninsular Malaysia

A new stratigraphic nomenclature is proposed for the approximately 600 m thick, mainly clastic transitional sequence between the underlying Mempelam Limestone and overlying Kubang Pasu/Singa Formation in northwest Peninsular Malaysia. This sequence represents shallow marine deposits of the continental margin of the Sibumasu Terrane during the Middle Palaeozoic (Devonian–Carboniferous). It is separated into several formations. The Timah Tasoh Formation is an approximately 76 m sequence consisting of 40 m of laminated tentaculitid shales at the base, containing Monograptus yukonensis Jackson and Lenz and Nowakia (Turkestanella) acuaria Alberti, giving an Early Devonian (Pragian–Emsian) age, and about 36 m of rhythmically interbedded, light coloured argillo-arenites. The Chepor Formation is about 90 m thick and consists mainly of thick red mudstone interbedded with sandstone beds, of Middle to Late Devonian age. A new limestone unit is recognized and named the Sanai Limestone, which contains conodonts of Famennian age. The Binjal Formation consists of red and white mudstone interbedded with sandstone beds showing Bouma sequences. The Telaga Jatoh Formation is 9 m thick and consists mainly of radiolarian chert. The Wang Kelian Formation is composed of thick red mudstone beds interbedded with silty sandstone, and contain fossils indicative of an Early Carboniferous (Visean) age. The succession was deposited on the outer shelf, with depositional environments vertically fluctuating from prodelta to basinal marine. The Devonian–Carboniferous boundary is exposed at Hutan Aji and Kampung Guar Jentik, and indicates a major regressive event during the latest Devonian.

A review of Lower and Middle Palaeozoic biostratigraphy in west peninsular Malaysia and southern Thailand in its context within the Sibumasu Terrane

Fossils from the Cambrian to Devonian rocks of southern Thailand, the Langkawi Islands, mainland Kedah, Perlis, north Perak and central West Peninsular Malaysia are listed and reviewed, and their stratigraphy and correlation reassessed. The hitherto anomalous record of the trilobite Dalmanitina from Malaysia is reviewed and found to be of latest Ordovician (Hirnantian) age, rather than Lower Silurian age as previously reported, and is considered a probable synonym of the widespread Mucronaspis mucronata. A new stratigraphical nomenclature is erected for part of the Langkawi, mainland Kedah and Perlis area successions, in which the term Setul Limestone (which stretched from the Ordovician to the Devonian) is abandoned and replaced by the Middle Ordovician Kaki Bukit Limestone, the late Ordovician and early Silurian Tanjong Dendang Formation, the Silurian Mempelam Limestone, and the early Devonian Timah Tasoh Formation, all underlying the paraconformity with the late Devonian Langgun Red Beds. There was a single depositional basin in the generally shallow-water and cratonic areas of southern Thailand, Langkawi, and mainland Kedah and Perlis, in contrast to the deeper-water basin of north Perak. Only Silurian rocks are dated with certainty within another basin in central West Malaysia, near Kuala Lumpur, which were also cratonic and shallow-water, although to the east in west Pahang there are basal Devonian deeper-water sediments with graptolites. The area is reviewed in its position within the Sibumasu Terrane, which, in the Palaeozoic, also included central and northern Thailand, Burma (Myanmar) and southwest China (part of Yunnan Province).

Palaeocurrents and provenance of the Mae Rim Formation, Northern Thailand: implications for tectonic evolution of the Chiang Mai basin

The Chiang Mai basin is the largest of a zone of rift basins that define the Northern Thailand Basin and Range Province. This province lies within the Shan Thai block of NW Indochina that extruded out of the India–Asia collision. The Mae Rim Formation crops out along the western side of the Chiang Mai basin. Detachment faults border the Mae Rim Formation on the west and north and juxtapose it against the high-grade Western Ranges metamorphic complex and its low-grade cover of Palaeozoic Shan-Thai rocks. Understanding the age and tectonic relationships between rifting, detachment faulting, ductile shear, uplift and exhumation of the Western Ranges metamorphic complex is critical to understanding the underlying deformational mechanisms that accompanied Indochina's extrusion. To better understand the palaeogeography of the Chiang Mai basin and its relationship to the Western Ranges metamorphic complex, several partial sections were measured, and palaeocurrent and clast-composition data from the Mae Rim Formation were collected. Poorly organized, immature conglomerates of the Mae Rim Formation probably represent alternating debris flows, sheet-flood, and braided channel deposits. The Mae Rim Formation probably accumulated in range-front alluvial fans, and graded rapidly into lacustrine deposits within the buried central part of the Chiang Mai basin. Except for the youngest strata, where gneissic clasts predominate, virtually all clasts in the Mae Rim Formation came from the low-grade metasedimentary rocks that form the cover of the Western Ranges metamorphic complex. Imbricated clasts indicate eastward palaeocurrents away from the metamorphic complex. Most of the Mae Rim Formation accumulated during the uplift of the Western Ranges but before erosion had breached the detachment fault. These new data suggest a tectonic history for the Chiang Mai basin that involved distinct phases of extension from late Oligocene to Quaternary, with at least two intervening periods of basin inversion.

A new Permian species of Mooreoceras (Cephalopoda: Orthocerida) from northwestern Peninsular Malaysia

A new orthocerid cephalopod species, Mooreoceras sibumasuense sp. nov., is described from the lowest part of the Chuping Formation in Bukit Tungku Lembu of the Perlis State, northwestern Peninsular Malaysia. The holotype of the species occurs in argillaceous limestone that is most likely late Kungurian (late Early Permian) in age and was deposited under cool-temperate water conditions on the Sibumasu Terrane of the eastern Cimmerian Continent. Most Permian species of Mooreoceras appear to be palaeobiogeographically confined to cool to cool-temperate palaeoclimate zones of the Australian Gondwana to Sibumasu region. Mooreoceras sibumasuense sp. nov. belongs to a group that probably survived due to isolation from high predatory stress in tropical to temperate seas. (Communicated by Tatsuro MATSUMOTO, M.J.A.)

New paleomagnetic constraints on the extrusion of Indochina: Late Cretaceous results from the Song Da terrane, northern Vietnam

Samples were collected for paleomagnetic investigations from the Upper Cretaceous Yen Chau Formation in the Song Da terrane (21.7°N, 103.9°E) bounded by the Ailao Shan–Red River fault system and Song Ma fault, in an attempt to examine extrusion tectonics of East Asia. Primary nature of the high-temperature (600–690 °C) component of magnetization from 13 sites is supported by a positive fold test. The tectonic corrected data provides the characteristic Late Cretaceous paleomagnetic direction for the Song Da terrane ( D=6.4°, I=32.0° with α 95=8.5°, N=13 sites), corresponding to a paleopole lying at 82.9°N, 220.7°E ( A 95=6.9°). Comparison with coeval paleomagnetic poles for the neighboring tectonic blocks indicates no latitudinal translation of the Son Da terrane with respect to the South China Block, whereas the Shan-Thai Block and the southern part of the Indochina Block revealed a southward displacement of 10.5±9.5° in latitude with respect to the Song Da terrane. We conclude that the southeastern segment of the Ailao Shan–Red River fault system to the east of the Dien Bien Phu fault is not a demarcation of the extruded Indochina Peninsula. The Indochina Block extruded probably along some faults between the Song Da terrane and the Khorat Plateau.

Long-lived Paleotethyan pelagic remnant inside Shan-Thai Block: Evidence from radiolarian biostratigraphy

Newly identified radiolarians from ribbon chert in the Mae Hong Son-Mae Sariang area, northwestern Thailand covered Early Carboniferous, Late Permian, and Middle-Late Triassic in age, which indicate that there was a pelagic basin during the Late Paleozoic and Triassic in this region together with the published radiolarian biostratigraphic data. This basin is joined with the Chiang Dao and Changning-Menglian oceanic basins, which represent the main oceanic basin of Paleotethyan Archipelago Ocean. The main oceanic basin was situated in the traditional “Shan-Thai Block”. Therefore, “the Shan-Thai Block” was not a single block during that stage, but composed of the Paleotethyan Ocean and two continental terranes that affiliated to Gondwana and Cathysian domains respectively.

Early Carboniferous radiolarians from north‐west Thailand: palaeogeographical implications

Moderately well‐preserved radiolarian assemblages are described from bedded cherts south of Mae Hong Son, north‐west Thailand. Twenty species and subspecies are identified, including one new species (Archocyrtium sashidai Feng sp. nov.). The assemblages belong to the middle Early Carboniferous Albaillella indensis and Eostylodictya rota zones. The new data suggest that there was a pelagic basin between the Shan‐Thai terrane and Gondwana during the Early Carboniferous. This implies, contrary to previous interpretations, that the Shan‐Thai terrane had already rifted apart from Gondwana during the Early Carboniferous.

The Padaeng Supergene Nonsulfide Zinc Deposit, Mae Sod, Thailand

The Padaeng deposit near Mae Sod in western Thailand was the first supergene nonsulfide zinc deposit in the world to be developed as a large modern mining operation. The mine and associated zinc smelter, operated by Padaeng Industry Public Company Ltd. since 1984, went into production with reserves of 4.59 Mt at a grade of 28.9 percent zinc with a 10 percent zinc cutoff. Current resources are 5.14 Mt at a grade of 12.0 percent zinc with a 3 percent zinc cutoff. The Padaeng deposit is hosted by a mixed carbonate-clastic sequence of Middle Jurassic age. The deposit occurs in the hanging wall of the Padaeng fault, a major northwest-trending structure that was active through Cretaceous and Tertiary tectonism and uplift. Nonsulfide zinc ore comprises dominant hemimorphite with minor smithsonite and hydrozincite. Strata-bound ore zones occur within a northwest-dipping, deeply weathered, dolomitic sandstone; steeply dipping and irregular karstic zones in underlying massive, silty dolomite are controlled by north-trending fracture zones. Sulfide zinc-lead mineralization of Mississippi Valley type occured extensively in the vicinity of the Padaeng mine, most notably the small resources at Pha De and Hua Lon. Mineral deposits are typically sphalerite rich with minor galena and pyrite, forming small-scale open-space fillings, veins, and replacements within hydrothermal dolomite. Mineralization is dominantly strata bound within a horizon of intense hydrothermal dolomitization that forms the stratigraphic hanging wall to the nonsulfide ore zones at Padaeng. The only significant sulfide at the Padaeng mine is within this unit. Only trace sulfide occurs peripheral to, or down dip of, strata-bound or steeply dipping, nonsulfide orebodies. Sulfide mineralization is believed to have accompanied Cretaceous uplift and deformation, related to the onset of oblique subduction beneath the western margin of the Shan-Thai terrane. The nonsulfide deposit is believed to have formed when a substantial body of sulfide ore was uplifted on the margin of the Mae Sod Tertiary intermontane basin, commencing in the middle to late Miocene. Zinc-bearing acidic supergene fluids, generated by oxidation of the precursor sulfide body, reacted with carbonate in the underlying stratigraphic section to precipitate hemimorphite and smithsonite. Fluids were channeled by permeable dolomitic sandstones and by steep fracture and fault zones. Acidic fluids promoted deep weathering and karst formation, allowing mineralization to extend down dip in sandstone units for at least 150 m and vertically for a similar distance in steep structural zones. Transport of zinc out of the precursor sulfide body was facilitated by a falling water table, owing to uplift of the Padaeng fault block and a change from wet tropical to monsoonal or semiarid climatic conditions. There is no evidence for significant in situ replacement of sulfide deposits, and the leached remnants of the precursor sulfide body have been removed by erosion. The supergene process of dissolution and reprecipitation of zinc in the host rocks increased zinc grades and separation of zinc from lead, producing an economically attractive deposit. Successful exploration for this type of deposit requires a good understanding of the controls on primary sulfide mineralization and a good knowledge of local neotectonism, uplift history, hydrogeology, climatic evolution, and weathering history.

Permian of Myanmar

Permo-Triassic carbonates with minor basal clastics cover extensive tracts of the Shan Plateau in the eastern part of Myanmar. These carbonates are grouped into the Permian Thitsipin Limestone Formation and the Late Permian–Early Triassic Nwabangyi Dolomite Formation. The Thitsipin Formation occurs as isolated masses, in many places faulted against older rocks. It is now known that there is a regional unconformity between the Thitsipin Limestone Formation and the underlying silici-carbonates of Devonian age in Shan State, and between the Thitsipin Limestone Formation and Carboniferous meta-siliciclastics in Kayah State, Mon State, Kayin State and Tanintharyi Division. Some of the Thitsipin limestone is dolomitized and passes transitionally upward into the Nwabangyi Dolomite Formation. Permian shelf-carbonates occur within two different sequences: the silici-carbonate sequence of the Shan–Thai Block and the meta-siliciclastic sequence of the Mergui Terrane, suggesting that the Permian limestones were deposited after the emplacement of the Mergui Terrane onto the southern margin of the Shan–Thai Block. This event occurred when the Shan–Thai Block was in the southern hemisphere.