Abstract A method is presented for integrating structural and alteration interpretations based on regional remote sensing magnetic and infrared spectral data. Integrated interpretations can provide insight about the controls that basement structural architecture exerts over porphyry mineralization. The method is illustrated by a study of the porphyry-endowed Kerman belt of Iran, for which structural interpretations of EMAG2 first vertical derivative magnetic data were refined using alteration lineaments interpreted from Landsat-8 infrared spectral data. This method makes use of regional linear alteration trends indicative of lithologic discontinuities to refine and to enhance the understanding of deep-seated structures interpreted from regional magnetic data. The integrated structural and alteration analysis of the Kerman belt of Iran highlights a first-order fault that is interpreted continuously at depth over approximately 500 km strike length and shows good spatial correlation with the location of most porphyry deposits and prospects. The analysis also allows for the visualization of a premineralization regional dilational zone that hosts the most prolific portion of the Kerman porphyry belt.

Abstract Two recent papers, “Utility of high-altitude infrared spectral data in mineral exploration: Application to northern Patagonia Mountains, Arizona,” by Berger et al. (2003), and “Mapping hydrothermally altered rocks at Cuprite, Nevada, using the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), a new satellite-imaging system,” by Rowan et al. (2003), make a distinctive mark on the use of airborne and satellite hyperspectral imaging as an exploration tool. These two papers deal with imaging of the Earth’s surface using the visible (0.4 μ m) to near infrared (2.5 μ m) part of the electromagnetic spectrum to map various mineral species. Depending on their structure and molecular bonding, minerals reflect and absorb the electromagnetic spectrum in unique ways. A large group of minerals have distinct electromagnetic signatures that make it possible to identify them from imaging systems that map the range of the electromagnetic spectrum between 0.5 and 2.5 μ m. These papers represent two distinct approaches. The first paper, by Berger et al., discusses the use of the AVIRIS (Airborne Visible Infrared Imaging Spectrometer) scanner, which provides high-resolution reflectance measurements in the spectral domain (224 channels between 0.4 and 2.45 μ m) and variable spatial resolution (20 m), dependent on aircraft altitude. The second paper, by Rowan et al., discusses the use of the ASTER satellite scanner, which offers a limited range of spectra at three spatial resolutions (15, 30, and 90 m). ASTER measures reflectance radiation in 3 bands within the 0.52- to 0.86- μ m range (visible-near-infrared) at 15-m spatial resolution, and 6 bands between 1.00 and 2.43 μ m (short wave infrared) at 30-m spatial resolution. Emitted radiation is measured in 5 bands between 8.125 and 11.650 μ m (thermal infrared) with a 90-m spatial resolution. The main advantage of the AVIRIS sensor is the level of spectral detail, which provides accurate measurements of reflectance and absorption features of minerals that enables detailed mineral mapping. Its main disadvantages, however, are the extensive processing required to make the reflectance spectra useful, and its limited spatial coverage and acquisition cost based on programmed flights. In contrast, the main advantage of the ASTER sensor is that it measures key portions of the visible, near-infrared, and thermal infrared spectra of minerals for large-scale mapping projects, whereas its main disadvantage is that the data represent only portions of the electromagnetic spectrum and some minerals cannot be distinctively mapped. In addition, the lower spatial resolution in the near-and thermal infrared portions of the spectrum makes it more difficult to map at detailed scales.

We present on- and offshore structural data from the Nazca-Panama plate boundary zone in the Gulf of Chiriquí and surrounding onshore areas of southwest Panama. Major offshore structures interpreted on multichannel seismic profiles from the Gulf of Chiriquí include Cébaco basin complex, a series of northeast-striking, Plio-Pleistocene half-grabens, and Montuosa basin, an asymmetric Plio-Pleistocene sag basin associated with a major strike-slip fault. We interpret Cébaco basin complex as a pull-apart basin between two major, left-lateral strike-slip faults that accommodate oblique motion between the Nazca plate and the mainland of southwestern Panama. Interpretation of regional seismic stratigraphic data indicates that the Plio-Pleistocene extensional phase that produced the Cébaco basin complex extended the area by about 7%. We studied outcrop-scale, conjugate strike-slip fault systems exposed on landmasses surrounding the Gulf of Chiriquí in order to place kinematic and age constraints on large-scale faults mapped on seismic profiles. Fault systems deforming Eocene to Lower Miocene sedimentary rocks on Coiba Island and the Azuero and Soná Peninsulas suggest an approximately northwest-southeast orientation of maximum extensional strain in an area that encompasses the offshore Cébaco basin complex. We propose three possible models to explain the observed pattern of strike-slip deformation observed in the Gulf of Chiriquí: (1) Neogene oblique subduction of the Nazca plate beneath Panama produces left-lateral strike-slip faulting and related northwest-oriented extension within the forearc (Gulf of Chiriquí) (2) Plio-Pleistocene shallow subduction/collision between the Cocos ridge and Costa Rica produces southwestward motion or “escape” of a Gulf of Chiriquí block that is detached from the rest of Panama by left-lateral strike-slip faults, and (3) Neogene bending of the Panama island arc following collision with the South American continent is accommodated in part by strike-slip motion and underthrusting along the southwest margin of Panama. Observed deformation may be a composite effect of more than one of these tectonic mechanisms.