Acoje and Masinloc Flashcards
Where is the Acoje Mine located?
In the Zambales ophiolite complex on the island of Luzon, Philippines.
What type of geological formation hosts the Acoje Mine?
The Zambales ophiolite, a fragment of oceanic crust and upper mantle emplaced during the Late Miocene.
What are the main ore minerals mined at Acoje?
Chromite and nickel.
What are the primary host rocks for chromite at Acoje?
Dunite and harzburgite in the ultramafic section of the ophiolite.
How did the chromite deposits at Acoje form?
Through magmatic processes, where chromite crystallized early from mafic-ultramafic magma and accumulated in layers or pods.
What is the role of dunite channels in chromite formation?
They acted as conduits for magma flow, facilitating the accumulation of chromite.
How did the nickel laterite deposits at Acoje form?
Through weathering of ultramafic rocks under tropical conditions, leading to the concentration of nickel and iron oxides.
What is the primary nickel-bearing mineral in the laterite deposits?
Garnierite, a nickel-bearing silicate mineral.
What are the two main zones in the nickel laterite profile?
The limonite zone (iron-rich) and the saprolite zone (nickel-rich).
What structural features control chromite deposition at Acoje?
Folds, faults, and shear zones within the ophiolite sequence.
What is the typical Cr2O3 content in high-grade chromite ore at Acoje?
50–60%.
What are the common textures of chromite ore at Acoje?
Massive, disseminated, or banded.
What is the typical nickel grade in the laterite deposits at Acoje?
1% to 2%.
What mining methods are used at Acoje?
Open-pit mining for laterites and underground mining for chromite.
What is the economic significance of the Acoje Mine?
It is a major producer of chromite and nickel, important for ferronickel and stainless steel production.
What tectonic event led to the emplacement of the Zambales ophiolite?
The Late Miocene tectonic emplacement of oceanic crust onto the continental margin.
What is the age of the Zambales ophiolite complex?
Approximately 10–15 million years (Late Miocene).
What are the main lithologies in the Zambales ophiolite?
Ultramafic rocks (harzburgite, dunite) and mafic rocks (gabbro, basalt).
What is the significance of the Acoje Mine in the Philippines?
It is one of the largest chromite producers in the country.
What are the key exploration targets at Acoje?
High-grade chromite pods and extensive nickel laterite profiles.
Where is the Masinloc ore deposit located?
In the Zambales ophiolite complex on the island of Luzon, Philippines.
What type of geological formation hosts the Masinloc deposit?
The Zambales ophiolite, a fragment of oceanic crust and upper mantle emplaced during the Late Miocene.
What is the primary ore mineral mined at Masinloc?
Chromite.
What are the primary host rocks for chromite at Masinloc?
Dunite and harzburgite in the ultramafic section of the ophiolite.
How did the chromite deposits at Masinloc form?
Through magmatic processes, where chromite crystallized early from mafic-ultramafic magma and accumulated in layers or pods.
What is the role of dunite channels in chromite formation?
They acted as conduits for magma flow, facilitating the accumulation of chromite.
What structural features control chromite deposition at Masinloc?
Folds, faults, and shear zones within the ophiolite sequence.
What is the typical Cr2O3 content in high-grade chromite ore at Masinloc?
50–60%.
What are the common textures of chromite ore at Masinloc?
Massive, disseminated, or banded.
What are the main gangue minerals associated with chromite at Masinloc?
Olivine, pyroxene, and serpentine.
What mining methods are used at Masinloc?
Open-pit mining and underground mining.
What is the economic significance of the Masinloc deposit?
It is a major producer of chromite, used in stainless steel, alloys, and refractory materials.
What tectonic event led to the emplacement of the Zambales ophiolite?
The Late Miocene tectonic emplacement of oceanic crust onto the continental margin.
What is the age of the Zambales ophiolite complex?
Approximately 10–15 million years (Late Miocene).
What are the main lithologies in the Zambales ophiolite?
Ultramafic rocks (harzburgite, dunite) and mafic rocks (gabbro, basalt).
What is the significance of the Masinloc deposit in the Philippines?
It is one of the largest chromite producers in the country.
What are the key exploration targets at Masinloc?
High-grade chromite pods within the ultramafic section of the ophiolite.
What type of ore deposits are found in Acoje?
Chromite (podiform chromite) and nickel laterite.
What major minerals are found in the Masinloc deposit?
Chromite, magnetite, and sulfides (pentlandite, pyrrhotite).
What is the key difference in chromite composition between Acoje and Masinloc?
Acoje: High Cr:Fe ratio chromite
Masinloc: High Al, low Fe chromite.
Which deposit is associated with lateritic nickel formation, and why?
Acoje—because weathering of ultramafic rocks (harzburgite and dunite) enriched the laterites with nickel and cobalt.
What host rocks dominate the Acoje and Masinloc deposits?
Acoje: Harzburgite, dunite
Masinloc: Dunite, pyroxenite.
Explain the tectonic setting of the Acoje deposit and its implications for ore formation.
Acoje formed in a supra-subduction zone (forearc mantle wedge), where magma differentiation produced podiform chromitites. Later, intense weathering led to nickel laterite enrichment.
Why does the Masinloc deposit contain high-alumina chromite instead of high Cr:Fe chromite?
Masinloc formed in a mid-ocean ridge or island arc setting, where deeper mantle melting and high-pressure fractionation favored the formation of high-Al chromite instead of high Cr:Fe chromite.
How does magmatic segregation contribute to the formation of Masinloc’s magnetite-rich chromitites?
During magmatic crystallization, chromite and magnetite separated from ultramafic magma, forming layered or stratiform chromite deposits.
If a new chromite deposit is discovered in Zambales with high Cr:Fe chromite and nickel laterites, which deposit (Acoje or Masinloc) would it resemble? Explain why.
It would resemble Acoje, because:
High Cr:Fe ratio suggests forearc mantle processes.
Presence of nickel laterite indicates intense lateritic weathering, which is common in Acoje but not in Masinloc.
