Hey -Rio-
Thank you very much for sharing that info, the Caroline looks like an absolutely top notch mine to explore, a best in class type of experience for safety, accessibility and interestingness.
It's very impressive that you actually brought an air quality monitor, but of all the hundreds of old mines I've investigated, the Caroline looks like one of the safest possible mines for expected ventilation and guaranteed lack of toxic gases. In a hillside mine with entrances at all levels like that, anything that is not flooded is guaranteed to naturally aspirate with the seasons, at least well enough to prevent any kind of fatal conditions from ever forming. If water can drain, so will any heavy gases, and if water can't drain, it will be flooded, like the conveyor level you mention. Meanwhile there are no light gases of concern in a hard rock gold mine with no coal anywhere within hundreds of miles, so there is no concern with trapped high spots.
I've done a fair bit of old mine exploring, it's an insatiable fixation for me, a compulsion, and the main thing I'm interested in when traveling. The Caroline just hit my short list, I will be checking it out in depth.
Other aspects relevant to safety: it's a new enough mine to not have suffered the kind of long term degradation that many older mines have undergone. Most of the wood will be relatively solid, air exposed rock should not be excessively rotten. And the mine is a rare example of a ramp accessible underground works, instead of being shaft or steep incline access only between the levels. This is a rare gem for getting to explore an old mine.