Geochemical variations of precursor and ore-related intrusive rocks associated with porphyry copper deposits in Sonora, northwestern Mexico
4
Citation
72
Reference
10
Related Paper
Citation Trend
Keywords:
Porphyritic
Batholith
Back-arc basin
Trace element
The intrusion of the Cassia batholith in Idaho was accompanied by clearly denned contact phenomena expressed by the impregnation of "igneous" material into quartzite, and in such a manner as to make it resemble granitic rock. While the magma crystallized as granodiorite, it sent forth emanations into the invaded rock and by progressive replacements produced therein a broad zone of porphyritic granite. As a result of the progressive granitization of the quartzites in the contact zone, the batholith is now about three times as large as it would have been had "replacement" not been a factor in its intrusion. It is altogether likely that the changes noted in the contact zone of the Cassia batholith may also be expressed in the crystalline schists in extensive metamorphic regions. The replacement origin of the microcline phenocrysts in the hybrid porphyritic granite also directs attention to the probability that the microcline phenocrysts in normal granitic rocks also may have been formed late by replacement.
Batholith
Porphyritic
Phenocryst
Microcline
Cite
Citations (8)
The late-Hercynian magmatic alignement of the Los Pedroches Batholith in South Central-Iberian Zone (Iberian Massif) exhibits a conspicuous dike swarm. Dikes are in chronological order: a) traquiandesite, b) dacite to rhyodacite, c) rhyolite, d) aplite, aplopegmatite and pegmatite, e) quartz, f) basic (diabase, lamprophyre).
Rhyolite dikes (granite to adamellite) form a number of lineal swarms oriented N120-130E. The main group extends almost undisturbed from near Belalcazar (Cordoba) to the Guadalquivir fault (Jaen). This array, ca. 130 km length and 2-12 km thick, is usually composed of 3 to 50 dikes cutting across the main plutonic facies of the Batholith.
Rhyolite dikes have the common granitic minerals, including zircon, apatite and ilmenite as accessories. According to their macroscopic features and petrography the dikes may be porphyritic microgranite, porphyritic rhyolite or porphyritic granophyre, whereas according to the mineral cheroistry the dikes range froro rhyolite-granite to alkali feldspar granite-rhyolite. The cheroical composition of studied rocks corresponds to peraluminous and calc-alkaline
terms of a K-rich alumino-cafemic calc-alkaline association.
The dike swarm cuts granite massifs of the Los Pedroches batholith intruded at ca. 300 ± 6 Ma (El Guijo pluton, Fernandez et al., 1990), but the emplacement is poorly constrained as inferred by K-Ar mineral ages of ca. 315 ±15 Ma (Bellon et al, 1979) and Rb-Sr whole rockage of 295 ± 18 Ma (Defalque et al., 1992). The dike swarm would result of subvolcanic intrusions genetically related to the late-Hercynian igneous activity that originated the Los Pedroches Batholith.
Batholith
Porphyritic
Dike
Massif
Dacite
Felsic
Cite
Citations (1)
Batholith
Porphyritic
Cite
Citations (93)
Iron oxide-copper-gold(IOCG) and porphyry copper deposits are all important exploration target due to their large-scale,high economic value.They are together generated in Chile subduction-related continental margin,including the world's large copper porphyry deposits,and have a sharp mineralization sequence in space-time from magnetite-apatite,IOCG,porphyry copper-gold to porphyry copper molybdenum deposits with tectonic-magmatic evolution.Large number of calc-alkaline magmatism and contemporary igneous rocks are an important foundation for formtion of mineralization.Shallow breccia pipes of IOCG deposits share with the alteration features of porphyry copper deposits.Gold-rich porphyry copper deposit have some similar characteristics and more transitional relation to porphyry deposits due to the key factors of evolution of magma intrusion and fluid.It is necessary to pay more attention to structure and alteration of rocks during the exploration.
Breccia
Cite
Citations (1)
SummaryElectrical methods have been applied to the search for porphyry copper and IOCG deposits since the early 1950s. While there is a generally accepted model of disseminated sulfides giving rise to a chargeability response, no clear association has been attached to what EM surveys may be responding to. Work in the early 1990s (Nickson 1993) showed the well-developed supergene blankets over a porphyry copper could be conductive; this observation was however, never applied formally to generally accepted porphyry targeting models. The presence of other conductive zones associated with porphyry copper deposits is even less well studied. On the geological side, while there is a vast body of literature describing porphyry copper deposits and how to discover them, in very few cases do these studies even speculate if anomalous concentrations of sulfides could be conductive. On the geophysical side, observations of unexpected conductivity associated with porphyry systems is sometimes noted but these observations typically stop short of suggesting that there could be a more general observation made that a new class of geophysical feature should be defined. The present study is felt to have gathered a sufficient number of case studies which show that a significant number of porphyry copper deposits posse a mineralogical character which can be identified with EM techniques. This thesis can have significant implications as to how porphyry copper are explored for, especially those at depths >500 m, a generally accepted cut-off for IP techniques.
Supergene (geology)
Reflection
Cite
Citations (2)
Abstract This paper investigates the reasons for the presence of both domed inselbergs (bornhardts) and boulder inselbergs (koppies) on the Matopos Batholith, Zimbabwe. XRF and microprobe analyses of rock samples from 16 bornhardts and 24 koppies have shown no significant chemical or mineralogical differences which might indicate greater weathering resistance of the bornhardts. Many bornhardts are located on massive bodies of slowly‐cooled porphyritic granite which were emplaced at a relatively late stage in the evolution of the batholith. The surrounding rocks are less porphyritic and appear to have been foliated during deformation associated with emplacement of the later bodies. The entire batholith has been affected by post‐emplacement tectonism which has created three major fracture systems. The morphological differences between bornhardts and koppies in this area are therefore considered to reflect differences in jointing which arise both from the primary igneous emplacement process and from tectonic deformation.
Batholith
Porphyritic
Cite
Citations (22)
The Precambrian Cachoeirinha-Salgueiro Fold Belt (CSF) located in the western portion of the states of Pernambuco and Paraiba is intruded, in its northern portion, by several coarsely porphyritic potassic calc-alkalic .batholiths. These batholiths were syntectonicaly unplaced in relation to the Brasiliano cycle (=Pan-African) and are commonly associated with potassium diorites suggesting coexistence and mixing between felsic and mafic magmas. In the Itaporanga batholith three petrographic domains-were mapped. A hybrid zone characterized by intense mechanical mixing of granite to granodiorite and potassium diorite magmas is located towards the border of the batholith. A commingling zone where felsic porphyritic granite to granodiorite and potassium diorite rocks are individualized at outcrop scale is located towards the center of the batholith. Finally a felsic porphyritic fades occur in the hybrid zone. The intense mechanical mixing observed in the hybrid zone developed migmatite-like structures (stromatic and less frequently agmatic), pillov -like structures, mafic enclaves with irregular shape and cuspate contacts between mafic and felsic rocks, suggesting diffusion of chemical species across contact. Major and trace element plotted against SiO 2 agree with a mixing model to explain the hybrid samples plotted at intermediate position between felsic and mafic rocks. Similarity among chemical analyses of amphiboles from potassium dioritic enclaves of the Itaporanga batholith and from the potassium diorite stock east of it suggest a common source for both magmas. This hypothesis is corroborated by similar REE patterns for potassium dioritic enclaves of the Itaporanga batholith and for the potassium diorite stock. The batholith shows a well developed foliation which dips towards its core suggesting that the present level of exposure represents the root zone of a diapir, where intense interaction between felsic and mafic magmas took place.
Batholith
Porphyritic
Felsic
Diorite
Cite
Citations (1)
Batholith
Hornblende
Porphyritic
Felsic
Cite
Citations (35)
The Precambrian Cachoeirinha-Salgueiro Fold Belt (CSF) located in the western portion of the states of Pernambuco and Paraiba is intruded, in its northern portion, by several coarsely porphyritic potassic calc-alkalic .batholiths. These batholiths were syntectonicaly unplaced in relation to the Brasiliano cycle (=Pan-African) and are commonly associated with potassium diorites suggesting coexistence and mixing between felsic and mafic magmas. In the Itaporanga batholith three petrographic domains-were mapped. A hybrid zone characterized by intense mechanical mixing of granite to granodiorite and potassium diorite magmas is located towards the border of the batholith. A commingling zone where felsic porphyritic granite to granodiorite and potassium diorite rocks are individualized at outcrop scale is located towards the center of the batholith. Finally a felsic porphyritic fades occur in the hybrid zone. The intense mechanical mixing observed in the hybrid zone developed migmatite-like structures (stromatic and less frequently agmatic), pillov -like structures, mafic enclaves with irregular shape and cuspate contacts between mafic and felsic rocks, suggesting diffusion of chemical species across contact. Major and trace element plotted against SiO2 agree with a mixing model to explain the hybrid samples plotted at intermediate position between felsic and mafic rocks. Similarity among chemical analyses of amphiboles from potassium dioritic enclaves of the Itaporanga batholith and from the potassium diorite stock east of it suggest a common source for both magmas. This hypothesis is corroborated by similar REE patterns for potassium dioritic enclaves of the Itaporanga batholith and for the potassium diorite stock. The batholiths shows a well developed foliation which dips towards its core suggesting that the present level of exposure represents the root zone of a diapir, where intense interaction between felsic and mafic magmas took place.
Batholith
Porphyritic
Diorite
Felsic
Cite
Citations (13)