Australia's great comet hunter

John Tebbutt was Australia's pre-eminent 19th-century astronomer who discovered two great comets of that century. Ragbir Bathal tells his story.     

Variability of mangrove ecosystems along the Brazilian coast

Brazilian mangroves extend from 4°30′N to 28°30′S, varying greatly in growth form, species distribution patterns, and stand structure, in spite of a limited floristic diversity. We divided the Brazilian coastline into eight units, within which physiographic and climatic conditions are relatively uniform, and described mangrove occurrence, species distribution and structural attributes characteristic of each segment. In general, greates mangrove coverage and greatest forest stature are found in areas with a large surplus of rainfall over potential evapotranspiration and macrotidal regimes. An exception was the segment containing the mouth of the Amazon river, where freshwater systems dominate over brackish or marine associations. We believe that the variability in species associations and the dominance of each in a given environment is predominantly determined by the characteristics of the landforms that can be colonized by each species in a given region. The type, size, and frequency of occurrence of available landforms is a function of the particular mix of fluvial, tidal, and wave energies found in a region. Different species colonize these sites depending on their adaptations and edaphic preferences. Climate affects mangrove colonization and growth. We suggest that Brazilian mangroves play a minor role in modifying the geomorphic setting; the spatial arrangement of the various forest types is a response to the underlying topography and edaphic conditions, and to the constraints imposed by climatic and hydrologic factors. The spatial arrangement of species does not necessarily show successional processes, but may be the result of direct and differential colonization on appropriate substrates.     

MinIdent: An application to the identification and classification of amphiboles

Summary Amphibole data in the MinIdent database (Smith andLeibovitz, 1986) were initially entered using species names quoted in the original source. The database has been updated by reclassifying these early data using the program AMPHTAB supplied by N. M. S. Rock and by adding supplemental data from the more recent literature, with the species names again checked using AMPHTAB. Associated MinIdent mineral identification software was utilized to determine which minerals in the database most closely resemble a series of unknown specimens chemically, as expressed in the Chemical Matching Index, CM, a relative figure-of-merit. Chemical data fromMogessie and Tessadri (1982) and Hawthorne (1983) were used to check the agreement between MinIdent and AMPHTAB for the classification of 221 unknown amphiboles.With 450 amphibole analyses entered and compiled in MinIdent, the name assigned by AMPHTAB showed the highest value of CM in MinIdent for 127 of the 221 unknown amphiboles (57.5°/x) and the second highest value for another 32 (14.5%). A chemically adjacent amphibole field had the highest value of CM for 59 of the 221 unknowns (26.7%), where chemically adjacent refers to a change in one chemical parameter. The greatest discrepancy between the two programs occurred in the hornblendes, with an agreement of just 20%, although for 58% of the unknowns the species with the highest CM in MinIdent was in a chemical field adjacent to the species name assigned by AMPHTAB. In many cases the disagreement between MinIdent and AMPHTAB could be ascribed to a lack of data in MinIdent.A comparison of the two programs suggests that the assignment of a single name to an unknown amphibole by AMPHTAB with no direct indication of its reliability may be; misleading. Standard analytical errors are frequently sufficient to overlap the arbitrary boundaries between amphibole species fields. In such cases it may be preferable to use a program such as MinIdent which, rather than assigning an arbitrary amphibole name, presents a list of 20 amphiboles with the degree of similarity between them and the unknown amphibole indicated. MinIdent offers the additional benefit of allowing input of other than chemical data and bases the match between unknown and standard data upon all input data. This will become more of an advantage as instruments such as automated refractometers become available for routine use.

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Zusammenfassung Ausgangspunkt war das Amphibol-Datenmaterial (Smith und Leibovitz, 1986) mit den dort verwendeten Artnamen. Diese Basisdaten wurden vervollständigt und erneuert durch Reklassifizierung mittels des AMPHTAB Programms, ergänzt durch N. M. S. Rock, und durch Hinzufügung weiterer Daten aus der neuesten Literatur, deren Speciesnamen wiederum mit AMPHTAB überprüft wurden. Außerdem wurde eine MinIdent Mineralidentifizierungs-Software verwendet, um die Minerale zu bestimmen, die in ihrem Chemismus am ehesten einer Serie von unbekannten Amphibol-Species entsprechen, wie sie im Chemical Matching Index (CM) aufscheinen. Zur Klassifikation von 221 unbekannten Amphibolen wurden chemische Daten von Mogessie und Tessadri (1982) verwendet um die Übereinstimmung zwischen MinIdent und AMPHTAB zu überprüfen.Unter den 450 in MinIdent zusammengestellten und eingegebenen Amphibolanalysen zeigen die bei AMPHTAB angegebenen die höchsten CM Werte, nämlich 127 von 221 unbekannten Amphibolen (57,5%) und weitere 32 (14,5%) die zweithöchsten Werte. Innerhalb eines chemisch benachbarten Amphibolfeldes hatten 59 der 221 unbekannten Amphibole (26,7%) die höchsten CM Werte, wobei unter achemisch benachbart die Änderung eines chemischen Parameters zu verstehen ist. Die größten Unterschiede zwischen den beiden Programmen traten bei den Hornblenden auf. Die Übereinstimmung lag bei nur 20%, obwohl bei 58% der unbekannten Amphibole die Species mit dem höchsten CM Wert in MinIdent in ein chemisches Feld zu liegen kamen, welches zu den bei AMPHTAB angegebenen Speciesnamen eine benachbarte Position einnimmt. Die Unterschiede zwischen MinIdent und AMPHTAB könnten in vielen Fällen auf ein Fehlen von Daten in MinIdent zurükzuführen sein.Ein Vergleich beider Programme deutet an, daß die Angabe eines Einzelnamens für ein unbekanntes Amphibol im AMPHTAB Programm ohne Angaben über die Zuverlässigkeit zu Mißverständnissen führen kann. Normale analytische Fehler können bereits dazu führen, daß die Grenzen zweier willkürlicher Amphibolfelder überlappen. In derartigen Fällen emphiehlt sich die Anwendung des MinIdent Programmes, welches eben nicht einen willkürlichen Amphibolnamen angibt, sondern eine Liste von 20 Amphibolen mit dem Grad ihrer Ähnlichkeit, und einem Hinweis auf den unbekannten Amphibol. MinIdent bietet den zusätzlichen Vorteil, daß man außer chemischen auch andere Daten eingeben kann, und stellt dann sämtliche Daten des unbekannten Amphibols den Standard Daten gegenüber. Dieser Klassifizierungsvorgang wird mit der zunehmenden Routineanwendung von automatischen Refraktometern verstärkte Anwendung finden.

     

Industrialisation in Fiji: Industrial structure and organisation

This paper analyses the significance, structure, and organisation of the manufacturing sector in Fiji, drawing on the author's earlier much larger study of industrialisation in Fiji. The latest Fijian census of industrial production (1984) and the author's 1983 survey of manufacturers in Fiji provide the main statistical basis of the study, which shows that the manufacturing sector is a moderately important component of the Fijian economy. It is dominated by resource industries, particularly food processing, but a wide range of manufacturing activities have, nonetheless, developed. There is a substantial number of small manufacturing establishments with a few large establishments, the latter, however, making an overwhelmingly important contribution to employment, gross output and value added. The market structure in the manufacturing sector is dominated by monopolies and oligopolies resulting from Fiji's small domestic market and its import substitution industrialisation strategy. There is an absence of informal sector activities in Fijian manufacturing, most firms being incorporated companies. The state has a major role as a direct producer in Fijian manufacturing. There are bound to be major changes in the manufacturing sector due to Fiji's current political crisis, but this paper does not address these because of the recency of the events and the consequent unavailability of relevant data.     

Acidic deposition impacts mediated by sulfur cycling in a coastal plain forest ecosystem

Deposition in the New Jersey Pinelands was very acidic (pH=4.17) and contained high levels of SO₂ ⁻² based on bulk deposition measurementsfrom July 1984–July 1986. Streamwater over the same interval in undisturbed watersheds was less acidic (pH =4.52) and had proportionately less SO₄ ⁻². A preliminary alkalinity budget for undisturbed watersheds suggested that SO₄ ⁻² retention within Pinelands watersheds accounted for a large portion of the total alkalinity generated and thereby lessened the impact of acidic deposition on surface waters. The only process capable of explaining the retention of SO₄ ⁻² was microbial sulfate reduction in the extensive wetlands surrounding Pinelands streams which occurred at high rates.     

The zircon-thorite mineral group in metasomatized granite,Ririwai, Nigeria 1. Geochemistry and metastable solid solution of thorite and coffinite

Summary At Ririwai, Nigeria, a biotite granite has suffered extensive post-magmatic metasomatism to produce albitized, microclinized, and greisenized rocks; the latter two lithologies form the wallrocks adjacent to tin-zinc vein-style mineralization. All the rock-types carry accessory amounts of thorite, locally accompanied by trace amounts of paragenetically late coffinite and xenotime. Petrographical and electron-microprobe data are presented for these minerals. In the biotite granite, thorite and coffinite range to high Zr contents (25.1 wt% ZrO₂ in thorite and 11.7 wt% in coffinite), exceeding the highest values previously reported in both minerals. In the lode wallrocks, yttrium contents range up to 13.9 wt% Y₂O₃ in thorite and 15.9 wt% in coffinite. From stoichiometric considerations, both minerals are inferred to contain OH. Petrographically, the thorites of the lode wallrocks are distinctive, and they are interpreted as having grown from the metasomatizing fluids. The albitized rocks and some of the lode wallrocks contain the thorites with the highest U contents, including one example of continuous zoning to coffinite. The unusual mineral compositions are interpreted as metastable solid-solution ranges formed from fluids that transported U, Th, Y and, over short distances, Zr.

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Die Zirkon-Thorit Mineral Gruppe in metasomatisiertem Granit, Ririwai, Nigeria. 1. Geochemie und metastable feste Lösungen des Thorit und Coffinit

Zusammenfassung In Ririwai, Nigeria, wurde ein Biotit-Granit durch extensive Metasomatose in albitisierte, mikroklinisierte und vergreisete Gesteine umgewandelt. In Mikroklin-Gesteinen und Greisen sitzt eine Zinn-Zink-Gangvererzung! Sämtliche Gesteinstypen führen Thorit als akzessorischen Gemengteil, stellenweise mit Spuren von spätgebildetem Coffinit und Xenotim. Petrographische und Mikrosonden-Daten dieser Minerale werden präsentiert. Im Biotit-Granit erreichten die Zr-Gehalte im Thorit und Coffinit Werte, wie sie bisher noch nicht bekannt waren (25.1 Gew.-% ZrO₂ im Thorit und 11.7 Gew.-% im Coffmit). In den Nebengesteinen reichen die Yttrium-Gehalte im Thorit bis 13.9 Gew.-% Y₂O₃, und im Coffinit bis 15.9 Gew.-%. Aus stöchiometrischen Überlegungen kann vermutet werden, daß beide Minerale OH enthalten. Petrographisch sind die Thorite aus den Nebengesteinen eindeutig definiert, und sie dürften aus metasomatischen Fluida entstanden sein. Die albitisierten Gesteine und auch einige Nebengesteine führen Thorite mit den höchsten U-Gehalten, darunter ein Beispiel mit einem kontinuierlichen Zonarbau bis zum Coffinit. Die ungewöhnlichen Mineralzusammensetzungen werden als metastabile feste Lösungen interpretiert, die aus Fluiden gebildet worden sind, welche U, Th, Y und über kurze Distanzen auch Zr transportiert haben.

     

The geology,mineralogy and geochemistry of the broomstock gold deposit,Kwekwe Greenstone Belt,Zimbabwe; Some implications for gold mineralization in jaspilite iron formations

Summary At Broomstock Mine, three types of gold mineralization have been identified: (i) jaspilite-hosted ore, (ii) ore confined to shear zones within meta-basalts, and (iii) supergene ore. The present study, which is focused on the jaspilite-hosted ore, revealed that areas carrying economic gold grades are characterized by fracturing, brecciation and abundant arsenopyrite-pyrite mineralization. The mineralization was introduced by hydrothermal fluids which used dilatant fractures in the jaspilites as channelways. Deposition of gold and sulfides occurred in response to changing P-T conditions and through chemical reactions of the fluids with the iron-rich jaspilites. Gold and accompanying elements may either originate from processes of intraformational remobilization, or they were derived from external, distant sources.

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Geologie, Mineralogie und Geochemie der Goldlagerstätte Broomstock im Kwekwe Greenstone Belt, Zimbabwe: Bedeutung für Goldvererzung in jaspitischen Eisenformationen

Zusammenfassung In der Broomstock Mine treten drei Typen von Goldmineralisationen auf: (i) Vererzungen in Jaspiliten, (ii) Vererzungen in Scherzonen, die Metabasalte durchsetzen, und (iii) supergene Vererzungen.Die vorliegende Untersuchung befaßt sich vornehmlich mit den Vererzungen der Jaspilite. Kartierungen und Beprobungen zeigten, daß ökonomische Goldgehalte an Be-reiche der Jaspilite gebunden sind, die tektonisch zerbrochen und brekziiert sind. Zudem treten in diesen Bereichen Arsenkies und Pyrit in hohen Konzentrationen auf. Die Mineralisation stellt den Absatz hydrothermaler Lösungen dar, die dilatante Bruchzonen innerhalb der Jaspilite als Zufuhrkanäle benutzten. Der Absatz der Sulfide und des Goldes erfolgte aufgrund sich ändernder P-T-Bedingungen und durch chemische Reaktionen zwischen den Lösungen und den eisenreichen Jaspiliten. Als Modell zur Herkunft des Goldes und der begleitenden Elemente wird entweder eine intraformationale Umlagerung, oder eine Zufuhr aus externen, entfernteren Quellen angenommen.

     

Canopy dieback in the upper montane rain forests of Sri Lanka

In 1978 a patch of dying upper montane rain forest had been observed on the slope of Thotupolakanda above Horton Plains. Patches in the upper montane rain forests of Sri Lanka were also recorded in 1980/81. All these sites were on windswept western slopes and ridges with stunted tree growth and shallow soil. From 1971 to 1983 Sri Lanka experienced some exceptionally dry years. The severe droughts of 1976 might have cause or “triggered” that dieback. After heavy rains between 1983 and 1986, these forests showed signs of recovery. Some trees had survived and sprouted again. Tree saplings were found, but regeneration was very low and further impeded by serious frost in February 1986. The influence of drought and frost clearly indicates the vulnerability of the stunted upper montane rain forest in the highest and wind-exposed regions of Sri Lanka.