Final answer:
The question seeks to determine the absolute age of 'intrusion H' through U-Pb geochronology based on a 235U to 207Pb isotope ratio in a zircon mineral. Without additional data or a specific decay rate, it is not possible to provide an exact age.
Step-by-step explanation:
The student is asking how to determine the absolute age of an intrusion known as 'intrusion H' by analyzing the ratio of 235U to 207Pb isotopes found in a zircon mineral sample. Given the isotope ratio of 25/75 for 235U and 207Pb, respectively, one needs to apply principles of U-Pb geochronology to calculate the age.
This type of radiometric dating is based on the decay of uranium into lead isotopes and has been instrumental in dating geological materials.
Knowing the half-life of 235U, which is 0.704 billion years, and the current isotope ratio, a calculation can be performed to find the amount of time that has passed since the zircon mineral in intrusion H formed. However, to provide an accurate answer, one would need additional data such as the decay rate or the initial ratio of isotopes for a precise calculation, neither of which was provided in the question.