Acoje and Masinloc

Question 1

Where is the Acoje Mine located?

Answer 1

In the Zambales ophiolite complex on the island of Luzon, Philippines.

Question 2

What type of geological formation hosts the Acoje Mine?

Answer 2

The Zambales ophiolite, a fragment of oceanic crust and upper mantle emplaced during the Late Miocene.

Question 3

What are the main ore minerals mined at Acoje?

Answer 3

Chromite and nickel.

Question 4

What are the primary host rocks for chromite at Acoje?

Answer 4

Dunite and harzburgite in the ultramafic section of the ophiolite.

Question 5

How did the chromite deposits at Acoje form?

Answer 5

Through magmatic processes, where chromite crystallized early from mafic-ultramafic magma and accumulated in layers or pods.

Question 6

What is the role of dunite channels in chromite formation?

Answer 6

They acted as conduits for magma flow, facilitating the accumulation of chromite.

Question 7

How did the nickel laterite deposits at Acoje form?

Answer 7

Through weathering of ultramafic rocks under tropical conditions, leading to the concentration of nickel and iron oxides.

Question 8

What is the primary nickel-bearing mineral in the laterite deposits?

Answer 8

Garnierite, a nickel-bearing silicate mineral.

Question 9

What are the two main zones in the nickel laterite profile?

Answer 9

The limonite zone (iron-rich) and the saprolite zone (nickel-rich).

Question 10

What structural features control chromite deposition at Acoje?

Answer 10

Folds, faults, and shear zones within the ophiolite sequence.

Question 11

What is the typical Cr2O3 content in high-grade chromite ore at Acoje?

Answer 11

50–60%.

Question 12

What are the common textures of chromite ore at Acoje?

Answer 12

Massive, disseminated, or banded.

Question 13

What is the typical nickel grade in the laterite deposits at Acoje?

Answer 13

1% to 2%.

Question 14

What mining methods are used at Acoje?

Answer 14

Open-pit mining for laterites and underground mining for chromite.

Question 15

What is the economic significance of the Acoje Mine?

Answer 15

It is a major producer of chromite and nickel, important for ferronickel and stainless steel production.

Question 16

What tectonic event led to the emplacement of the Zambales ophiolite?

Answer 16

The Late Miocene tectonic emplacement of oceanic crust onto the continental margin.

Question 17

What is the age of the Zambales ophiolite complex?

Answer 17

Approximately 10–15 million years (Late Miocene).

Question 18

What are the main lithologies in the Zambales ophiolite?

Answer 18

Ultramafic rocks (harzburgite, dunite) and mafic rocks (gabbro, basalt).

Question 19

What is the significance of the Acoje Mine in the Philippines?

Answer 19

It is one of the largest chromite producers in the country.

Question 20

What are the key exploration targets at Acoje?

Answer 20

High-grade chromite pods and extensive nickel laterite profiles.

Question 21

Where is the Masinloc ore deposit located?

Answer 21

In the Zambales ophiolite complex on the island of Luzon, Philippines.

Question 22

What type of geological formation hosts the Masinloc deposit?

Answer 22

The Zambales ophiolite, a fragment of oceanic crust and upper mantle emplaced during the Late Miocene.

Question 23

What is the primary ore mineral mined at Masinloc?

Answer 23

Chromite.

Question 24

What are the primary host rocks for chromite at Masinloc?

Answer 24

Dunite and harzburgite in the ultramafic section of the ophiolite.

Question 25

How did the chromite deposits at Masinloc form?

Answer 25

Through magmatic processes, where chromite crystallized early from mafic-ultramafic magma and accumulated in layers or pods.

Question 26

What is the role of dunite channels in chromite formation?

Answer 26

They acted as conduits for magma flow, facilitating the accumulation of chromite.

Question 27

What structural features control chromite deposition at Masinloc?

Answer 27

Folds, faults, and shear zones within the ophiolite sequence.

Question 28

What is the typical Cr2O3 content in high-grade chromite ore at Masinloc?

Answer 28

50–60%.

Question 29

What are the common textures of chromite ore at Masinloc?

Answer 29

Massive, disseminated, or banded.

Question 30

What are the main gangue minerals associated with chromite at Masinloc?

Answer 30

Olivine, pyroxene, and serpentine.

Question 31

What mining methods are used at Masinloc?

Answer 31

Open-pit mining and underground mining.

Question 32

What is the economic significance of the Masinloc deposit?

Answer 32

It is a major producer of chromite, used in stainless steel, alloys, and refractory materials.

Question 33

What tectonic event led to the emplacement of the Zambales ophiolite?

Answer 33

The Late Miocene tectonic emplacement of oceanic crust onto the continental margin.

Question 34

What is the age of the Zambales ophiolite complex?

Answer 34

Approximately 10–15 million years (Late Miocene).

Question 35

What are the main lithologies in the Zambales ophiolite?

Answer 35

Ultramafic rocks (harzburgite, dunite) and mafic rocks (gabbro, basalt).

Question 36

What is the significance of the Masinloc deposit in the Philippines?

Answer 36

It is one of the largest chromite producers in the country.

Question 37

What are the key exploration targets at Masinloc?

Answer 37

High-grade chromite pods within the ultramafic section of the ophiolite.

Question 39

What type of ore deposits are found in Acoje?

Answer 39

Chromite (podiform chromite) and nickel laterite.

Question 40

What major minerals are found in the Masinloc deposit?

Answer 40

Chromite, magnetite, and sulfides (pentlandite, pyrrhotite).

Question 41

What is the key difference in chromite composition between Acoje and Masinloc?

Answer 41

Acoje: High Cr:Fe ratio chromite Masinloc: High Al, low Fe chromite.

Question 42

Which deposit is associated with lateritic nickel formation, and why?

Answer 42

Acoje—because weathering of ultramafic rocks (harzburgite and dunite) enriched the laterites with nickel and cobalt.

Question 43

What host rocks dominate the Acoje and Masinloc deposits?

Answer 43

Acoje: Harzburgite, dunite Masinloc: Dunite, pyroxenite.

Question 44

Explain the tectonic setting of the Acoje deposit and its implications for ore formation.

Answer 44

Acoje formed in a supra-subduction zone (forearc mantle wedge), where magma differentiation produced podiform chromitites. Later, intense weathering led to nickel laterite enrichment.

Question 45

Why does the Masinloc deposit contain high-alumina chromite instead of high Cr:Fe chromite?

Answer 45

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.

Question 46

How does magmatic segregation contribute to the formation of Masinloc’s magnetite-rich chromitites?

Answer 46

During magmatic crystallization, chromite and magnetite separated from ultramafic magma, forming layered or stratiform chromite deposits.

Question 47

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.

Answer 47

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.