1,721,175 research outputs found
Nuove metodologie didattiche per la diffusione del geoturismo nelle scuole: il progetto Aliakmon
Full text linkINTRODUZIONE
La divulgazione al pubblico delle Scienze della
Terra non può prescindere dall’individuazione di
percorsi e metodologie idonee alla loro diffusione
nelle scuole di ogni ordine e grado. Questa
diffusione deve, però, avvenire attraverso l’utilizzo
di tecniche e metodologie nuove che permettano
di fare breccia negli interessi degli studenti, in
modo da poter raggiungere dei risultati positivi dal
punto di vista didattico.
PROGETTO GECO
Il progetto GECO nasce con lo scopo di
introdurre tecniche di ancoraggio innovative nel
presentare nelle scuole dell’infanzia, elementari,
medie inferiori e superiori tematiche di interesse
geologico.
Il primo obiettivo, promosso attraverso il
progetto, ha riguardato un percorso didattico per le
scuole medie superiori, articolato secondo uno
schema modulare che meglio permette di adattarlo
alle esigenze delle singole scuole. I moduli previsti
sono:
Incontro con gli studenti a scuola sotto
forma di conferenza dialogata con
videoproiezioni (modulo 1);
Sviluppo del progetto in singole classi con
uno o più incontri con il geologo (modulo
2);
Visite accompagnate presso siti di
interesse geoturistico (modulo 3).
Tra le metodologie introdotte per raggiungere il
successo formativo, particolarmente innovativo si
presenta l’utilizzo del romanzo “C’est l’Afrique” di
G. Grieco: un giallo catalogato come intrigo
industriale, che sviluppa una trama avvincente,
legata al lavoro di un geologo impegnato in studi
minerari in Madagascar. In essa confluiscono sia
informazioni e curiosità geologiche che la
descrizione dell’attività svolta dal geologo che
consente di comprendere l’importanza del metodo
e del rigore scientifico in questa disciplina.
L’incontro con gli studenti, sotto forma di
conferenza, viene incentrato sulle tematiche del
libro, accompagnato da immagini relative alle aree
descritte nel romanzo, ed in una cornice volta a
enfatizzare l’importanza della conoscenza del
territorio che si va a visitare in viaggi di qualsiasi
tipo.
Le fasi successive, in classe e attraverso visite
guidate, fanno perno sulla conoscenza del proprio
territorio (nel caso specifico la Lombardia) da
un punto di vista geologico e ambientale, e,
prendendo spunto dalla prima fase, prevedono un
percorso di visita a siti di interesse geoturistico.
Scopo fondamentale di questa fase è la
comprensione della storia geologica del territorio,
ma anche dell’attività svolta, oggi o in passato ,
dall’uomo nella sua interazione con l’ambiente.
La modularità del percorso permette una
fruizione adeguata alle esigenze della scuola. In
particolare il modulo (1) è stato finora sviluppato
con successo in 4 scuole, due licei classici e due
licei scientifici, il modulo (3) è stato sviluppato in
due scuole, un liceo scientifico e un gruppo misto
classico-scientifico e il modulo (2), il più
complesso, articolato e oneroso in termini di
tempo, è in fase di organizzazione per lo sviluppo
nel prossimo anno scolastico.
Un secondo obiettivo del progetto è indirizzato
alle scuole dell’infanzia e alle scuole elementari.
Questa parte del progetto, in corso di
sperimentazione presso la scuola dell’infanzia
Alessandrini di Zibido San Giacomo, in provincia di
Milano, prevede l’utilizzo di personaggi inventati
con stretto collegamento al mondo geologico,
fiabe ad argomento ambientale e naturalistico, che
permettano ai bambini un primo approccio
semplice, ma comunque corretto, ed efficace alle
tematiche geologiche.
Il progetto rivolto ai bambini è anch’esso
organizzato con la medesima modularità,
cercando di far comprendere i concetti geologici di
base con esperienze dirette che vanno dal
disegno alla manipolazione di materiali naturali, i
quali possono poi essere riutilizzati anche in un
secondo momento e autonomamente direttamente
dall’insegnante. Al primo approccio, che avviene in
classe, segue poi un percorso geoturistico che
utilizzerà una tipologia di geositi particolarmente
195
significativa in Lombardia, quella dei parchi
naturali realizzati tramite il recupero ambientale di
cave e miniere dismesse e quella dei massi
erratici, ai quali sono da sempre legate
testimonianze e legende di particolare presa sui
bambini, con possibilità di visita guidata ad uno dei
tanti geositi di questo tipo della regione.
RINGRAZIAMENTI
Gli Autori ringraziano la 0111 Edizioni, che ha
curato la pubblicazione di “C’est l’Afrique” e
Matteo e Samuele Hess per le illustrazioni e
l’organizzazione dei laboratori didattici.
BIBLIOGRAFIA
GRIECO G: (2012) – C’est l’Afrique. 0111 Edizioni,
Cocquio Trevisago, 195 pp.
19
Geochemical trends within Madagascar chromite ores
No full textThe most important chromitite deposits of Africa are mainly located in South Africa, in the well known Bushveld complex, nevertheless Madagascar hosts some important chromitite deposits making Madagascar the world's 10th largest chromite producer. Kraomita Malagasy, the state-owned mining company, produces a chromite concentrate grading between 48 and 50 wt% Cr2O3 with 0.002 to 0.003 wt% P2O5 and lumpy chrome ore grading from 42 to 44 wt% Cr2O3. The main chromitite deposits of Madagascar are located in Andriamena, Befandriana and Tamatave regions and are related to archean basic-ultrabasic intrusions set in the central zone of the island. The mineralized regions present different geochemical and textural features that have influenced the explotaition and the general developing of chromite mining industry of Madagascar. Since strong quality parameters are required for the commercialization of both concentrate and lumpy products, a detailed chemical and textural analysis of such mineralization has been focused on understanding quality profile of these ores in ordrer to maximize future exploitation that strongly depends on chrmical and textural features of the ore itself. The Andriamena complex, located at the southern end of the Tsaratanana Mineral Field, has been the leading chrome producing region of Madagascar for the last decades. In Andriamena complex most of the chromite production comes from three mines: Ankazotaolana mine is characterized by a series of ultramafic lenses hosted by a gneissic rock of archean age. Chromitite shows values of C2O3 wt% between 35 and 40 with a Cr/Fe ratio up to 2.7; Bemanevika mine, characterized by a series of parallel lenses at different depth, has an average C2O3 content of 40 wt% and a Cr/Fe ratio of 2.3. Recent estimates predict 2.6 Mt of reserves for this area; the small deposit of Telomita has been recently reopened to increase the production. Telomita is charachterized by a C2O3 content similar to that of Ankazotaolana and a Cr/Fe ratio of 2.2. Befandriana district represents another strategic zone where chromitite lenses, ranging from few meters up to 10 meters in thickness, are highly massive, with C2O3 close to 53 wt% and Cr/Fe ratio close to 2.6. Tamatave district was the first to be exploited in the ’60 of last century and is characterized by highly deformed and metamorphosed chromitite lenses located in two main sites: Ambodiriana and Ranomena. Generally Tamatave chromitites show a low C2O3 content, close to 30 wt% and a Cr/Fe ratio lower than 1.5. Some important differences among studied ores have been highlightet by textural and chemical analyses. Andriamena chromitites show an average good quality, but with differences between mines. Befandriana ores show the best quality due to their massive texture together with high Cr2O3 content of chromite. Chromitite from Tamatave results to be absolutely unsuitable due to the low C2O3 content of chromite. On the other hand a surplus value of Tamatave chromitite is the presence of Platinum Group Minerals (PGM) mainly of laurite or complex solutions observed both included in chromite grains as well in the matrix. In general main chromite ores of Madagascar show a trend of decreasing Cr2O3 content from north to south, related to differences in ore genesis, that strongly affects ore quality for exploitation
Environmental study of Reps sulfide mine dumps, Mirdita District, Northern Albania
No full textThe mine and processing site of Reps operated until 1994 in the Fan valley, about 20km NE of Rreshen, Northern Albania. The mine dumps host sulfide-rich tailing materials resulting from the copper concentration processes. These tailing dumps are issues of environmental concern because of their proximity to the river, the presence of acid drainageproducing minerals and the unstable conditions of the piles. The aim of this work is to evaluate the release of potentially toxic elements (PTE) in the local environment through a geochemical survey of the two main piles, respectively named Reps1 and Reps2. We collected 46 solid samples and 17 water samples representative of the upstream flow, drainage and downstream delivery. Analyses have been conducted in order to characterize (i) the mineralogy, grain size and bulk chemical composition of the earthen samples; (ii) the concentration of PTE either in solid materials and waters; (iii) the presence and persistence of acid drainage. The features of the earthen materials have been defined by grain size and bulk elemental (ICP) composition, pH measures and in situ permeability tests. Microscopy, XRD and MPA analyses have also been performed on selected samples. The mineralogical and geochemical analyses have been performed on the granulometric fraction <2mm. The physical and chemical parameters of the water samples have been investigated through pH-Eh measurements and atomic emission spectrometry. The acid drainage production and the neutralising capacity were evaluated for a set of samples through the Acid Base Account (ABA) test. Moreover, we assessed the spatial relations between the geochemical variables using dedicated mapping softwares. The comparison between the pH analyses on solid samples reveals a stronger acidity of the waste materials of the Reps2 dump (pH=2.4-3.7), with respect to Reps1 (pH=3.2-4.3). Such a difference is due to a higher content of sulfides in the Reps2 samples. These contain a mixture of pyrite, marcasite, minor chalcopyrite, sphalerite and enargite, with associated silicates, oxides (Fe and Fe-Mg spinels) and sulphates (gypsum, barite). Secondary phases comprise hydrated Fe-sulfates and hydroxides. The mineralogical composition of these samples is reflected in the average concentration of S (14.9%) and hazardous metals such as Cu (4430 ppm), Zn (1970 ppm), and As (660 ppm). The drainage water samples show very low pH values (2.3-2.7), with respect to the upstream waters (pH=6.7-7.8). This acid character is associated to a high concentration of ions, the highest values being those of Zn (up to 100 ppm), Cu (up to 20 ppm) and Mn (up to 20 ppm). Our preliminary results on the potential acid drainage production include a total H2SO4 release of 588.087t and a predicted buffering time of 230 000 years. Our investigations at Reps show that this site undergoes a general widespread pollution due to the storage of sulfur and PTE-rich fine grained material in strong disequilibrium with the local morphology and adjacent to a main river that works as a collector of highly acid PTE-rich phases drainage water
Metamorphic redistribution of Cr within chromitites and its influence on chromite ore enrichment
No full textMineralogical and chemical characters of ore strongly affect the efficiency of chromite sand physical concentration. Usually chromite ore enrichment is based on the assumption that all Cr in the rock is hosted within chromite, but alteration in metamorphic conditions can lead to partial redistribution of Cr from chromite to silicates. Such redistribution was studied on the Vavdos chromite deposit (Greece) where more than 3% of whole rock Cr(2)O(3) can be found in silicates. The effect of Cr(2)O(3) redistribution is to lower the efficiency of gravity plants as Cr(2)O(3) contained in silicate phases will be preferentially discharged into the tailing during enrichment. Tests confirm the effect of Cr redistribution on enrichment and show that preferential separation of different silicates does not occur or is negligible. As the redistribution of Cr within the rock is not indicated by any change in whole-rock chemistry only the study of mineralogy, texture and mineral chemistry of the ore can provide a reliable basis for final product quality and Cr(2)O(3) recovery prediction
Determinazione dell'Acid Mine Drainage nel cantiere Valle Giove di Rio Marina (Isola d'Elba, LI)
No full textL’attività mineraria nell’Isola d’Elba è documentata fin da epoca pre-romana ed è correlata prevalentemente all’estrazione di minerali di ferro dai distretti di Capoliveri e Rio Marina. Il cantiere Valle Giove, oggetto del presente studio, è una miniera a cielo aperto con superficie di circa 1 km2, caratterizzata da una mineralizzazione a ematite + pirite ± blenda e calcopirite in lenti e filoni metrici. Tale sito è stato coltivato dal 1950 al 1981 ed attualmente è gestito dal Parco Minerario dell’Elba e dal Parco Nazionale dell’Arcipelago Toscano che lo utilizzano a fini escursionistici. Il cantiere è ubicato a monte e a ridosso dell’abitato di Rio Marina. L’ampiezza dell’area interessata dai lavori minerari e, conseguentemente, gli ingenti volumi dei materiali di risulta, rendono necessaria la caratterizzazione ambientale del sito e la determinazione dei fenomeni di acid mine drainage (AMD), anche in considerazione del recente termine dei lavori estrattivi. Sebbene i fenomeni di AMD siano solitamente associati ad aree minerarie con paragenesi a solfuri dominanti, la presenza di laghetti acidi e con alte concentrazioni di metalli è indizio dell’instaurarsi di processi di drenaggio acido legati alla distribuzione disomogenea dei solfuri che accompagnano la paragenesi a ossidi dominanti. Il presente studio analizza le problematiche connesse al drenaggio acido di miniera del sito mediante:
1. il calcolo dei volumi di materiale estratto e dei volumi di materiale riportato in discarica mineraria attraverso digitalizzazione, georeferenziazione ed analisi 3D delle carte topografiche del cantiere relative a diversi anni; 2. il campionamento dei terreni secondo uno schema a griglia (EPA, 2002) a maglia quadrata di lato pari a 100 m; 3. la caratterizzazione chimica dei terreni mediante analisi XRF; 4. la realizzazione di carte isopotenziali dei parametri di quantificazione dei processi di AMD (MPA, ANC e NAPP) mediante procedura AMIRA (IWRI & EGI, 2002); 5. la realizzazione di carte di isoconcentrazione dei metalli determinati con analisi ICP-AES.
I risultati ottenuti evidenziano come, anche in un sito minerario costituito prevalentemente da ossidi, i fenomeni di AMD possano creare un problema di primaria importanza a livello ambientale. L’esame complessivo dei dati ottenuti permette di eseguire: 1. la stima della durata nel tempo dei fenomeni di drenaggio acido; 2. la valutazione della composizione dei terreni e del loro possibile ruolo nei processi di AMD; 3. l’identificazione delle sorgenti di contaminazione, dei punti di produzione di acque acide e dei loro percorsi; 4. la proposta di eventuali interventi di ripristino ambientale
Chromitite alteration in serpentinite mélanges of Nurali and Kalkan massif (Russia)
No full textStudies on the genesis and evolution of Cr-mineralization in ophiolites usually do not consider the metamorphic processes that influenced the mineralization in later stages. Kalkan and Nurali chromitites from Urals mélanges exhibit different alteration. During post-serpentinization reactions Al diffuses out of magmatic spinel leaving behind a ferritchromite and promoting the formation of chlorite aureoles (Mellini, 2005). Kimball (1990) describes the alteration of spinel to ferritchromite and the formation of chlorite by the reaction:
MgAl2O4 +4MgO+3SiO2 4H2O = (Mg5Al)(AlSi3O10)(OH)8
with MgO, SiO2 and H2O coming from the fluid. At Kalkan post-serpentinization processes led to the formation of chlorite and ferritchromite by reaction of fluid with spinel and serpentine, with MgO and SiO2 coming from serpentine. Only rare serpentine relicts testify the serpentinization stage. At Nurali no evidences of chlorite and ferritchromite formation have been observed and post-serpentinization processes led to partial reabsorption of chromite. Serpentinization did not affect chromite and led to the formation of magnetite as coronae around chromite crystals or as small scattered magnetite grains in the matrix. According to the mineral chemistry of the involved phases we propose the following reaction for ferritchromite formation:
2(Mg0.60Fe0.40)(Cr1.30Al0.70)O4 +
3/2(Mg2.57Al0.32Fe0.11)Si2O5(OH)4 + H2O + 1/12O2→
7/6(Fe0.60Mg0.40)(Cr1.85Fe0.08Al0.07)O4 +
1/2(Mg9.18Fe0.34Al1.60Cr0.88) (Al2Si6)O20(OH)16.
Magnetite formation during serpentinization without involving chromite can be described by the reaction:
4(Mg1.8Fe0.2)SiO4 + 2(Mg0.9Fe0.1)SiO3 + 6H2O + 1/6O2→ 3Mg3Si2O5(OH)4 + 1/3Fe3O
Ore minerals and biogeochemical characters of Piazza copper mine area (La Spezia, Italy)
No full textApplication of an innovative beneficiation technique to Krasta chromite ore (Albania) for the production of high grade – low silica chromite sand
No full textThe Mirdita ophiolite is located in the northern ophiolite belt of Albania. Based on differences in the internal stratigraphy and chemical composition of the crustal units, two types of ophiolites have been recognized in the Mirdita ophiolite, namely the Western Mirdita Ophiolite (WMO) and the Eastern Mirdita Ophiolite (EMO) (Dilek et al., 2008). Boninitic dikes and lavas crosscut and/or overlie earlier extrusive rocks in the EMO (Beccaluva et al., 1994). The crustal section of the WMO has MORB affinities, whereas that of the EMO predominantly shows SSZ geochemical affinities. The extrusive sequence in the EMO consists of pillowed to massive flows ranging in composition from basalt and basaltic andesite in the lower section to andesite, dacite, and rhyodacite in the upper part (Bortolotti et al., 1996). Large peridotite massifs are exposed at the western and eastern ends of the Mirdita ophiolite. Plagioclase-bearing peridotites are frequently observed in the WMO, whereas harzburgite is dominant in the EMO (Beqiraj et al., 2000).
In this work, we focus on Bulqiza peridotite massif located in the EMO, because it has economically important chromite ores. Chromite is an important mineral used in the metallurgy, chemistry and refractory industries and often requires enrichment processes to achieve the chemical parameters for different markets.
This work deals with disseminated chromite ore samples collected at Krasta Mine, located in the central southern part of the Bulqiza Massif. First of all the samples, having an average Cr2O3 content of 23.66 wt%, were enriched using spirals and shaking tables at Krasta plant. The first chromite sand concentrate has 46.58 wt% Cr2O3 and 10.35 wt% SiO2. In order to meet the very demanding chemical parameter requirements for refractory market chromite first concentrate sand was re-enriched using a combination of dry magnetic and gravity separation at the pilot plant of Omega Foundry Machinery LTD. in Peterborough (UK). In a second step sand was enriched using a drum magnet. New concentrate was then enriched in a third step by means of an Inclined Fluidised Separator (IFS) that works in dry conditions using an air cushion as fluidisation agent.
Preliminary results show that the pilot plant is able to strongly re-enrich the primary concentrate sand, producing a final concentrate sand with up to 60.01 wt% Cr2O3 and 2.43 wt% SiO2 with a tail that is still suitable for the steel market (Fig. 1).
Fig. 1. Three steps Krasta chromite ore enrichment: spirals and shaking tables at Krasta plant (white symbols), drum magnet (grey symbols) & IFS (black symbols) at Peterborough pilot plant. Square = feed, triangles = concentrates and circles = tails. First and second concentrates are the feeds of the following steps.
References
BECCALUVA, L., COLTORTI, M., PREMTI, I., SACCANI, E., SIENA, F., ZEDA, O. (1994): Ofioliti, 19, 77–96.
BEQIRAJ, A., MASI, U., VIOLO, M. (2000): Exploration and Mining Geology, 9, 149–156.
BORTOLOTTI, V., KODRA, A., MARRONI, M., MUSTAFA, F., PANDOLFI, L., PRINCIPI, G., SACCANI, E. (1996): Ofioliti, 21, 3–20.
DILEK, Y., FUMES, H., SHALLO, M. (2008): Lithos, 100, 174–209
Al-Spinel-sulphide bearing dikes and the fate of chromium in marginal reaction zones at Balmuccia
No full textThe Balmuccia peridotite massif is one of the subcontinental mantle peridotite bodies intruded in the mafic-ultramafic Ivrea-Verbano complex in the Western Alps, Northern Italy. The Balmuccia body consists of dominant foliated lherzolites crosscut by several generations of pyroxenite dikes, approximately belonging to an earlier “Cr-diopside suite” and a later “Al-augite suite”. These dike suites are interpreted as mineral segregations from melts which percolated into the lherzolite, refertilized it and caused focused dunitization of the host peridotite. Our study is focused on some thin, cm- to dm-thick pale grey-violet dikes presumably belonging to the late-stage Al-augite suite and intersecting the lherzolite mass at its eastern margin, near the intrusive contact with the Ivrea-Verbano complex. These dikes often show a spotted texture due to the segregation of abundant coarse vitreous black spinel phenocrysts. The mineral assemblage is both Al- and sulphide-rich. The silicate-oxide assemblage includes dominant clinopyroxene (diopside-augite) and blue-green, transparent Al-rich spinel, with minor Ti-rich Na-K pargasite amphibole, Al-bearing orthopyroxene (enstatite), accessory Ti-rich phologopite and plagioclase and rare olivine (intergrown with spinel droplets). Abundant Fe-Ni-Cu sulphides (pentlandite, phyrrotite, chalcopyrite and bornite) are widely disseminated across the dikes both as mm-sized polyphase nodules interstitial to the silicate-spinel matrix and as tiny, locally extremely abundant drop-like inclusions in spinel. Assemblages containing bornite exclusively occur as inclusions in spinels, which host a redox-dependant equilibrium pentlandite-chalcopyrite-bornite association. The richness in Ni sulphides copes with the scarcity of olivine in this association and is one of the interesting features of these dikes. Another curious feature involves the margins of the dikes. The contacts with the host lherzolite are sharp but not tectonic and are characterized by lateral passage from dike-related undeformed to lherzolite-related, variably foliated assemblages (olivine, ortho- and clino-pyroxenes, fine-grained dark brown spinel and rare amphibole). A visual inspection of the host lherzolite/grey dike contact zones showed a peculiar, progressive change in colour of the spinel from dark brown, in “distal” position, to green transparent near the dike margin. That was the most visible evidence of the interaction between lherzolite and intruding dikes, as an actual reaction zone is not easy to recognize texturally. Analytical transects across these mm- to cm-sized “contact zones” by means of microprobe showed that there may be a cryptic reaction zone. The lherzolite phases do record some changes in major element composition, and in particular spinel, pyroxenes and amphibole show variations in Chromium concentration, among others. Across the reaction zones lherzolite spinel vary their Cr content from about 19 wt% Cr2O3 to <1%. They also decrease their Fe2+ content whereas Al and Mg are enriched. Clinopyroxene shows a variable “response” to this reaction zone as it shows a tendency to Cr depletion coupled with Ti enrichment and fluctuations in alkalis. Accessory amphibole crystals in lherzolite show a trend of Cr depletion and Ti enrichment as well as a variability in Al and Na contents towards the dike margin. Cr is rather low in lherzolite orthopyroxene, however it shows a tendency to Cr and Mg depletion (and Fe enrichment) towards the dike contact. Olivine tends to be more forsteritic in a distal position. Ongoing and future analytical investigations are aimed to characterize and verify the meaning and the extent of this Cr-depleting Al-enriching and dike-lherzolite metasomatic interaction. Of particular interest is the fate of Cr, one of the economic elements enriched (after mobilization from a source) in relation to metasomatic processes, e.g., dunitization, affecting peridotites
- …
