Colloform Structures Research Articles

Multi-Analytical Characterization of Stone Relics from Meili Section of the Ancient Tea Horse Road in Yunnan, China

The stone relics in the Meili section of the ancient Tea Horse Road in Yunnan, China, are important for Sino-Tibetan cultural heritage. However, these relics were exposed to the risk of hydraulic erosion due to the construction of a hydroelectric power station, and thus protecting these relics is now imperative. Preliminary investigations and analyses of stone relics are crucial for their subsequent conservation and restoration. Thus, in this study, multi-analytical characterization including the microstructure, mineralogical characteristics, elements, and chemical compositions of the stone relics was conducted using optical microscopy (OM), scanning electron microscopy-energy dispersive spectrometry (SEM-EDS), polarized light microscopy, x-ray diffraction (XRD), and attenuated total reflection-Fourier transform-infrared spectroscopy (ATR-FTIR). In addition, the contaminants and pigments on the surfaces of the stone relics were identified and analyzed by Raman spectroscopy. OM, SEM and Raman spectroscopy indicated that the surface contaminants mainly comprised of moss and soil dust, and some of the stone relics exhibited porosity and weathering. Polarized light microscopy revealed that the mineralogical morphology of stone samples mainly appeared as allotriomorphic, hypidiomorphic, and colloform structures. ATR-FTIR, and XRD confirmed that the stone relics mainly consisted of quartz, muscovite, illite, and chlorite. In addition, Raman spectroscopic analysis showed that the pigments on the relic surfaces included chalk, barium white, langite, green earth, amorphous carbon black, chrome red, and chrome yellow. The findings of this study may provide scientific support for the conservation of the stone relics.

Geochemistry of cobalt-rich ferromanganese crusts from the Perth Abyssal Plain (E Indian Ocean)

Geochemistry of cobalt-rich ferromanganese crusts from the as-yet-unexplored Dirck Hartog Ridge (DHR), a linear bathymetric feature of poorly understood origin, located in the centre of the Perth Abyssal Plain (PAP), is described for the first time, based on 3 samples analyzed with XRF, ICP-MS and EPMA. Mean bulk concentrations of Fe and Mn were 20.8 and 18.4 wt%, respectively; individual crust layers, however, proved chemically variable. The mean concentration of metals of the highest economic potential (Cu + Ni + Co) was 0.69 wt%. The mean total rare earth elements (REE) and yttrium (ΣREY) contents in the samples (1908 mg/kg) proved moderate. The crusts showed strong positive Ce anomalies, negative Y anomalies and a low YSN/HoSN ratio (mean 0.56). Observations on the texture and chemical composition of the crust samples studied allowed us to distinguish two major and two subtypes of representative colloform structures built of laminae. The Type I colloform structures showed the Mn/Fe ratio to range from 0.86 to 5.69, the ranges in Type II colloform structures being 0.49–2.47 (Subtype II-1) and 6.91–221.42 (Subtype II-2). The Subtype II-2 colloform structures were enriched in Ni (up to 7.31 wt%). The Co and Cu concentrations showed a high variability, 0.03–1.64 and 0.03–0.22 wt%, respectively. According to the current genetic models and discrimination diagrams, the crusts studied were classified as hydrogenetic, although individual laminae and groups of laminae could be regarded as diagenetic or hydrothermal.

Relationship between CO2-dominated fluids, hydrothermal alterations and gold mineralization in the Red Lake greenstone belt, Canada

Abstract The Red Lake greenstone belt is one of the foremost Au mining camps in Canada and hosts the world-class Campbell-Red Lake Au deposit. Belt-scale hydrothermal alteration is characterized by proximal ferroan dolomite zones associated with Au mineralization surrounded by distal calcite zones, both being accompanied by potassic alterations (sericite, muscovite, and biotite). At the Campbell-Red Lake and Cochenour deposits Au mineralization (in particular high-grade ore) is associated with silica and sulfides (especially arsenopyrite) that replace carbonate ± quartz veins and the host rocks. The prevalence of carbonic fluid inclusions and rare occurrence of aqueous-bearing inclusions in carbonate–quartz–Au veins in the Campbell-Red Lake deposit, and the consistency of homogenization temperatures of carbonic inclusions within individual fluid inclusion assemblages (FIA), have been interpreted to indicate that H2O-poor, CO2-dominated fluids were responsible for the carbonate veining and Au mineralization. Further studies of fluid inclusions in carbonate–quartz veins within and outside the deformation zone hosting the Campbell-Red Lake deposit (the Red Lake Mine trend) including the Cochenour Au deposit, the Redcon Au prospect, and outcrops in the distal calcite zone also reveal the dominance of carbonic fluid inclusions in vein minerals. These studies indicate that CO2-dominated fluids were flowing through fractures during carbonate vein formation and Au mineralization both within and outside major structures. The carbonic fluid may have been initially undersaturated with water, or it may have resulted from phase separation of an H2O–CO2–NaCl fluid. In the latter case, phase separation modeling indicates that the initial fluid likely had X CO 2 values larger than 0.8. Calculations based on hydrothermal mineral assemblages indicate X CO 2 values in the host rocks from 0.025 to 0.85, reflecting a change from CO2-dominated fluids in the fractures (veins) to H2O-dominated fluids in the host rocks away from the fractures. The CO2-dominated fluids were likely advected from granulite facies in the deeper crust, whereas the H2O-dominated fluids were derived from the ambient host rocks of amphibole to greenschist facies. Calculations based on CO2 requirements and source constraints indicate that the mineralizing fluids were likely two orders of magnitude more enriched in Au than the commonly assumed values of a few μg/L, which may explain why the Campbell-Red Lake deposit has a very high-grade of Au (average 21 g/t for the whole deposit and 81 g/t for the Goldcorp High-Grade zone). Fluid inclusion data suggest that the carbonate veining and Au mineralization likely took place at depths from 7 to 14 km. The development of crustiform–colloform structures in the carbonate ± quartz veins, which was previously interpreted to indicate relatively shallow environments, may alternatively have been related to extremely high fluid pressures and the CO2-dominated nature of the fluids, which could have enhanced the brittle properties of the rocks due to their high wetting angles.

REMNANT COLLOFORM PYRITE AT THE HAILE GOLD DEPOSIT, SOUTH CAROLINA: A TEXTURAL KEY TO GENESIS

Auriferous iron sulfide-bearing deposits of the Carolina slate belt have distinctive mineralogical and textural features—traits that provide a basis to construct models of ore deposition. Our identification of paragenetically early types of pyrite, especially remnant colloform, crustiform, and layered growth textures of pyrite containing electrum and pyrrhotite, establishes unequivocally that gold mineralization was coeval with deposition of host rocks and not solely related to Paleozoic tectonic events. Ore horizons at the Haile deposit, South Carolina, contain many remnants of early pyrite: (1) fine-grained cubic pyrite disseminated along bedding; (2) fine-grained spongy, rounded masses of pyrite that may envelop or drape over pyrite cubes; (3) fragments of botryoidally and crustiform layered pyrite, and (4) pyritic infilling of vesicles and pumice. Detailed mineral chemistry by petrography, microprobe, SEM, and EDS analysis of replaced pumice and colloform structures containing both arsenic compositional banding and electrum points to coeval deposition of gold and the volcanic host rocks and, thus, confirms a syngenetic origin for the gold deposits. Early pyrite textures are present in other major deposits of the Carolina slate belt, such as Ridgeway and Barite Hill, and these provide strong evidence for models whereby the sulfide ores formed prior to tectonism. The role of Paleozoic metamorphism was to remobilize and concentrate gold and other minerals in structurally prepared sites. Recognizing the significance of paragenetically early pyrite and gold textures can play an important role in distinguishing sulfide ores that form in volcanic and sedimentary environments from those formed solely by metamorphic processes. Exploration strategies applied to the Carolina slate belt and correlative rocks in the eastern United States in the Avalonian basement will benefit from using syngenetic models for gold mineralization.

Sea-floor sulfides at the Hoydal volcanogenic deposit, central Norwegian Caledonides

The Hoydal volcanogenic massive sulfide deposit is associated with thick basaltic sheet flows toward the middle of a 1- to 2-km-thick, low-metamorphic, inverted, Lower Ordovician ophiolitic volcanite sequence in the central Norwegian Caledonides, just east of the major (25+ million metric tons) orebody at Lokken.Hoydal is one of the very few Scandinavian Caledonian strata-bound volcanogenic massive sulfide deposits which retains dominantly sea-floor depositional features, due to the minimal effects of later deformation and metamorphism. This study documents these features and compares them with those of recently formed and presently forming sea-floor sulfides.The layered massive sulfides at Hoydal are closely related to a sheetlike feeder zone as well as to extensive jasperoid layers and fault-scarp talus deposits. A palinspastic reconstruction relates the ores to sea-floor deposition along elongated, fissure-controlled, hydrothermal conduits; the talus breccias, involving sulfides, jaspers, and the volcanites, are considered to be due to movements along the feeder-fissure-fault system.Chemically the ore is dominated by Fe, Zn, and Cu, the two latter elements being highly variable and showing no significant correlation with each other. Ag is correlated with Cu, suggesting that most Ag is contained in chalcopyrite. Au shows a strong association with both As and Sb, and tennantite is suggested as a possible Au bearer.Investigations of ore textures have led to definition of several stages of mainly sulfide deposition. An early period of fine-grained colloform pyrite (+ chalcopyrite, sphalerite, and galena) deposition succeeded an earlier phase in which tabular pyrrhotite was probably formed. The colloform pyrite phase was succeeded conformably by coarser grained, clean, crystalline, sub- to euhedral pyrite, deposited in cockadelike structures outside the colloform structures. Contemporaneously, recrystallization of parts of the colloform pyrite produced (internally) euhedral, often poikilitic, pyrite.Both these noncolloform pyrites are attributed to a period of higher temperature conditions resulting from the sealing-off of cold seawater from the rising hydrothermal fluids. These conditions led further to the deposition of chalcopyrite as both open-space fillings and replacement of early-formed sulfides, accompanied by chalcopyrite disease in earlier sphalerite. The last main stage of sulfide deposition introduced the major part of the sphalerite apparently by open-space filling.Comparisons with present-day sea-floor sulfides, as described in the literature, reveal certain special features of the Hoydal sulfides. In common with the major orebody at Lokken, they appear to have been deposited in connection with a phase of vigorous volcanic activity, consequent upon the intrusion of new, hot, mafic magma to a high level in the oceanic crust which gave rise to large-scale hydrothermal convective systems.The main period of high-temperature chalcopyrite deposition was followed by a phase when hot solutions, deficient in Cu and Fe, caused redissolution of parts of the sulfides deposited earlier and the formation of a highly porous, residual pyrite + or - chalcopyrite ore. This was filled in and cemented by late, low Fe sphalerite and quartz introduced by low-temperature solutions during the waning stages of hydrothermal activity.Marked enrichment of elements such as Zn, Pb, Ag, Au, and Sb, relative to Cu and Fe, seems to be due to the purging of the last-mentioned elements from the solutions by large-scale deposition of chalcopyrite and pyrite within the underlying oceanic crust.

Petrography and Diagenesis of Silcrete from the Kalahari Basin And Cape Coastal Zone, Southern Africa

ABSTRACT Silcrete is widely distributed in southern Africa and occurs both in genetic association with deeply weathered bedrock (weathering profile type) and as a significant component of the Cenozoic Kalahari Beds where it has formed through silicification of a variety of continental deposits (nonweathering profile type). Silcrete fabrics are classified into four major types: GS (grain-supported--skeletal quartz grains in contact), F (floating--skeletal grains `floating' in matrix), M (matrix skeletal grains < 5% of volume), and C (conglomeratic--detrital component containing pebbles). F and M fabric types are subdivided on the presence/absence of glaebules. Replacement by silica of a precursor matrix can account for the development of all four fabric types, but at least some GS and C fabr c silcretes have formed by passive silica precipitation in packing voids. Glaebules and colloform features predominantly composed of concentrations of anatase and iron oxide are common in weathering profile silcretes, but their precise origin is uncertain. Authigenic silica is present as megaquartz, microquartz, length-slow and length-fast chalcedony (predominantly in void-fills), cryptocrystalline silica and opal-CT depending on the silica and ionic concentrations of pore waters, pH, and host sediment characteristics. Diagnostic petrographic features, including glaebules, colloform structures, and chalcedonic vugh-fills, may be used in conjunction with geochemical data and sedimentary associations to interpret silcretes in the stratigraphic record with respect to weathering profile types (formed in humid, low pH environments) or nonweathering profile types (formed in high-pH ? semiarid to arid environments).

Origin of Chert in Permian System in Southwestern Utah and Northwestern Arizona: ABSTRACT

Within the Permian System in southwestern Utah and northwestern Arizona, the Brady Canyon Member of the Toroweap Formation and the Fossil Mountain and Harrisburg Members of the Kaibab Formation contain five different forms of chert. These chert forms provide information about the origin and emplacement of chert in the Permian System. The forms present are: rounded chert nodules, ribbon chert, silicified burrows, disseminated chert, and massive chert that grades into limestone. Sources of chert are attributed to upwelling of deep bottom waters, silica-derived from freshwater mixing with saline water in deltaic complexes, and precipitation of silica through biological processes. Examination of fossiliferous rounded chert nodules, silicified burrows, ribbon chert, disseminat d chert, and stringers of chert, indicate that deposition was the result of secondary solution moving through areas with greater porosity. Disseminated chert, found in the Fossil Mountain Member, was deposited in the areas where the porosity was greatest. Massive chert in the Harrisburg Member formed at the water table where dissolution of the limestone occurred. This chert layer was then exposed to erosion. Chert emplacement occurred following the partial dolomitization of the limestone early in the diagenetic history. Some chert appears to have been deposited as secondary cement in the carbonate rock following cementation and dolomitization. Chert horizons in the upper part of the Kaibab Formation suggest that chert may have developed much later during an erosional cycle. This is suppo ted by colloform structures and gradation from a massive chert down to limestone. End_of_Article - Last_Page 525------------

Ferromanganese nodules from the devonian of the montagne noire (S. France) and West Germany

Ferromanganese nodules (equivalent to Recent manganese nodules) are described from the Upper Devonian griotte (red pelagic limestone) of the Montagne Noire (S. France) and the Cephalopodenkalk of the Rheinisches Schiefergebirge, West Germany. They occur as encrustations, commonly exhibiting colloform structures, around skeletal material and limestone clasts. The nodules are associated with encrusting foraminifera and a development in the sublittoral environment is envisaged. Chemically, the ferromanganese nodules are depleted in manganese relative to iron, compared with Recent nodules, a loss which is attributed to diagenetic migration of manganese. Electron probe studies show that manganese covaries positively with calcium, but negatively with iron and silicon. Diagenetic enrichment of hematite occurs in the griotte at hardground horizons where two periods of mineralization can be established. The Devonian ferromanganese nodules show that solution of nodules has not occurred on burial.

Silcretes and Associated Silica Diagenesis in Southern Africa and Australia

ABSTRACT Five types of silcrete are recognised in Australia and Southern Africa: terrazzo, conglomeratic, Albertinia, opaline and fine-grained massive, and quartzitic. Of these the first is the primary and most abundant form. The second and third types are derivatives of it, but the final two are distinct and much rarer. The terrazzo variety is mostly pale buff or yellowish grey, but may also be green or purplish brown. It consists of a framework of angular to subrounded quartz grains, some showing effects of solution, set in a matrix of amorphous, cherty or opaline silica containing abundant leucoxene. The leucoxene is a marked characteristic, and commonly forms colloform structures. The conglomeratic type consists of brecciated terrazzo type in a silcrete matrix of similar colour or bright r d. In the Albertinia type quartz detritus is almost absent. The rarer forms are mostly pure common opal or chalcedony, either massive or porous. The quartzitic type is the response of a sedimentary orthoquartzite to the silcrete-forming process. Many occurrences can be explained in terms of profile formation, silica being made available from elsewhere within the profile, and attention is drawn to the profile displayed on Spilsby Island, South Australia. Silica-rich solutions rising to meet downward percolating solutions with NaCl, Na2SO4, Fe2O3 or MgO or of lower pH, could cause the silica deposition. Very widespread occurrences may have formed by accumulation through evapo-transpiration. The quartzitic type forms by authigenic overgrowths in detrital quartz grains.

Geology of the Caribou Deposit, Bathurst, New Brunswick

The Caribou deposit occurs in a mixed volcanic–sedimentary zone which is transitional between graphitic argillite and silicic tuffaceous rocks. The silicic tuffaceous rocks form the core, and the graphitic argillite the outside, of the steeply plunging Caribou synform.The Ore Zone Unit consists of the volcanic–sedimentary transition zone and the sulfides. The Caribou deposit consists of three or more en echelon lenses of pyrite – sphalerite – galena – chalcopyrite and footwall disseminated sulfides. Sulfide zoning in the deposit indicates that the stratigraphic top is towards the silicic volcanic rocks. The deposit has a galena–sphalerite zone on the silicic volcanic side and the hangingwall contact is sharp. There is a chalcopyrite-rich zone on the sedimentary side and the contact is indistinct. Very fine spheres, cubes, and framboids of pyrite in both the deposit and the sedimentary wallrocks, as well as pyrite colloform structures in the deposit, appear to be relict primary or diagenetic structures.All the rocks, including the sulfides, have been regionally metamorphosed to lower greenschist facies and contain a pervasive slaty cleavage or schistosity, which is the earliest imprint of structural deformation. Pyrite, sphalerite, galena, chalcopyrite, arsenopyrite, quartz, stilpnomelane, and sericite are in a granoblastic intergrowth typical of metamorphosed sulfides. This early structural deformation has fractured and granulated pyrite and, to a limited extent, sphalerite; and chalcopyrite, galena, and sphalerite flowed plastically. The early slaty cleavage or schistosity has been deformed by minor structures and folded into the Caribou synform.Many features of the Caribou deposit and similarities to other volcanic-associated stratiform base metal deposits indicate a syngenetic origin involving submarine deposition of sulfides derived from volcanic, exhalative, hydrothermal solutions and possibly as pyroclastic debris.

Silver mineralization in the Mineral District, Washington County, Idaho

Mottled, blotched, fine-grained, unimpressive in the hand specimen, the ore in the Ag deposits in the little-known Mineral district near the Snake River in Washington County, Idaho, when viewed under the microscope, is found to possess extraordinary textural and structural features and a mineralogy that is unique to the state. The ore occurs as fillings and replacements along complex zones of fracturing in volcanic rocks of pre-Tertiary age and was formed close to the surface at temperatures mainly below 135 degrees C. Minerals, most of which are distinguishable and identifiable microscopically, include pyrite, marcasite, sphalerite, wurtzite, tetrahedrite, chalcopyrite, galena, and, in 1 deposit, also stannite, cylindrite, bournonite, and boulangerite. The Fe and Zn sulfides show globular and botryoidal development with radial and concentric structures indicative of colloidal deposition. Because of the influence of these colloform structures on the deposition of the other, noncolloidal minerals, and also because of the more or less selective replacement of the ore minerals by late calcite, the textural and structural relations of the ore are complicated and of more than usual interest. Abundant permeation and replacement by late calcite has been responsible for the mottled and blotched appearance of the ore. The Ag probably had its source in the tetrahedrite and galena; the ore mined in the past had probably been enriched in supergene silver sulfides.

Geology and iron ores of Steep Rock Lake [Ontario

Mining operations at Steep Rock Lake since 1945 have yielded about ten million tons of high-grade iron ore and have cast new light on the geology of this long-famous Precambrian area. The productive length of this most-recently discovered of the Lake Superior ranges should exceed four miles and ore intersections have been obtained at depths down to 2,000 feet below the old lake bed, implying that potential reserves must be measured in hundreds of millions of tons.The Steeprock group lies unconformably upon a granitic complex (Laurentian) and consists of:5. Interbanded flows, tuffs, and sediments4. Ashrock (a basic pyroclastic containing minor flows and tuffs)3. The orezone2. Limestone and dolomite (in part showing algal and other organic (?) structures1. Basal conglomerate (not everywhere present)All these formations (together with younger basic intrusives) have been steeply tilted, more or less altered, and show foliation or brecciation in appropriate rock types. Such features (plus sporadic pyritic replacement lenses along and near the hanging-wall of the orezone, as well as recrystallization, modification, and minor migration of the iron ores) are ascribed to the activities of a post-Steeprock (Algoman) batholith that outcrops two miles to the west. Several major faults cross the area, the largest of which has caused a strike separation of more than two miles in the Steeprock group.The orezone holds all the known iron ore-bodies, is up to several hundred feet in width, shows remarkable continuity and uniformity wherever explored, and is made up of two members. The stratigraphically lower part is chiefly manganiferous waste (averaging more than 2 percent Mn) with minor iron ore, resting residually in erosional disconformity on the underlying leanly manganiferous and ferruginous limestone and dolomite. The upper part of the orezone carries negligible manganese and is composed chiefly of goethite with a few relatively narrow bands of cherty, sandy, and aluminous sediments. The ores show a variety of breccia, vuggy, and colloform structures. The most common type of breccia has fragments of very fine-grained goethite surrounded either by coarsely crystalline goethite or specularite or by earthy hematite. A pisolitic facies locally present along the hanging-wall of the orezone contains gibbsite and resembles a ferruginous bauxite.The field relations, mineralogy, and paragenesis suggest that the ore-bodies represent sedimentary limonite of Steeprock age, brecciated by compaction and folding, with the more finely comminuted matrix recrystallized or modified by hydrothermal solutions, locally effecting migration of iron.

EPITHERMAL MINERALIZATION AT THE LAST CHANCE AND HORNSILVER MINES, LAVA CREEK DISTRICT, BUTTE COUNTY, IDAHO

The epithermal deposits in the Lava Creek district are confined to a zone of structural weakness in Tertiary volcanics which facilitated intrusion of Miocene magma and circulation of ore-bearing solutions. After widespread sericitization, chalcedonization, pyritization, and local alunitization had initiated the first of two main stages of mineralization, pyrite, marcasite, sphalerite, wurtzite, galena, and chalcedony were deposited from solutions whose flow was controlled by minor structural adjustments at the source and along the channelways. Following a more marked structural reopening a second assemblage consisting of minor and variable amounts of quartz, barite, pyrite, stannite, tetrahedrite, famatinite, enargite, klaprothite, chalcopyrite, aikinite, and dickite were added. Lack of equal permeability of fracture zones during mineralization resulted in considerable variation in substance of individual lodes. Those of present commercial interest contain a notable concentration of lead and zinc sulfides. Characteristics of the mineralization indicate that the early solutions were alkalic and moderately hot, but with the formation of alunite they became and remained acidic and mostly below 135° C. Intimate associations of pyrite-marcasite and sphalerite-wurtzite afford evidence of a delicate balance between temperature and acidity changes with some fluctuations of one or the other and a gradual rise in temperature at the close of the stage. Colloform structures in the iron and zinc sulfides suggest colloidal phenomena. Solutions remained acidic during the second stage of deposition but had a higher temperature than during the earlier stage.

Microscopic Colloform Structures in “Mud Balls” at Waiotapu, New Zealand

A Recent paper in this journal by K. P. Oakley (1940) has drawn attention to certain structures in Recent rhyolitic ashes of Malaya, and contraverts the earlier view that these structures represent sponge spicules. Oakley suggests tentatively that most of them are the casts of minute spherical and tubular hollows in the material of the ashes. It may be of interest, therefore, to describe comparable material from New Zealand which appears to support this suggestion.