What is the black staff that is used for the sages jutsu.

What I think it is:

Ruyi Jingu Bang
It's described of being made of "black iron" with two gold bands round it near the ends. It is the magical weapon of Sun Wukong in "Journey to the West"

In a way this has appeared in the manga as Monkey King Enma's Transformation: Adamantine Staff, but that was only a transformation (Imitation) and not the real thing.

Jingu Bang has the power to change its size, multiply itself, and fight according to the whim of its master.

What power connected to the sage has the ability to do this? Chakra rods.

Chakra rods are the Ruyi Jingu Bang.

Jingu Bang is a Ruyi which is a ceremonial sceptre in Chinese Buddhism. Which the sages staff is also connected to.

The Sage's staff:

The sages staff has six rings representing the Six Perfections, a six ring khakkhara is carried by a Bodhisattva (a bodhisattva is anyone who, motivated by great compassion, has generated bodhicitta, which is a spontaneous wish to attain Buddhahood for the benefit of all sentient beings)

Six Perfections:
  1. Dāna pāramitā: generosity, giving of oneself
  2. Śīla pāramitā : virtue, morality, discipline, proper conduct
  3. Kṣānti (kshanti) pāramitā : patience, tolerance, forbearance, acceptance, endurance
  4. Vīrya pāramitā : energy, diligence, vigor, effort
  5. Dhyāna pāramitā : one-pointed concentration, contemplation
  6. Prajñā pāramitā : wisdom, insight

Most novice monks carry a four ring staff which represent the Four Noble Truths. An easy way to explain the truths, they represent overcoming your negative emotions.

I believe that the sage having six rings on his staff when he fought the Juubi means that he has already overcome his emotions & started to spread his teachings. I've also said before that you unlock the Rinnegan by overcoming your emotions, which is the opposite of the Sharingan.

I think the chakra rods are allow a Rinnegan user to control their paths because all of them are the sages staff & the sages staff is the Jingu Bang.

The Sage's power: the Rinnegan & Sasuke's search for the "truth"

The Sage's Rinnegan has four "rings"

The Rinnegan "rings" could also represent the Four Noble Truths.

Sasuke's journey has followed the four noble truths & the 'third power' could represent the 'third truth'

The first two truths:
Dukkha = suffering, anxiety, stress & unsatisfactoriness
The first noble truth is the truth of dukkha. The Pali term dukkha is typically translated as "suffering", but the term dukkha has a much broader meaning than the typical use of the word "suffering". Dukkha suggests a basic unsatisfactoriness pervading all forms of life, due to the fact that all forms of life are impermanent and constantly changing. Dukkha indicates a lack of satisfaction, a sense that things never measure up to our expectations or standards.

The second noble truth is the truth of the origin of dukkha. Within the context of the four noble truths, the origin of dukkha is commonly explained as craving conditioned by ignorance.

The third truth is Cessation:
Cessation is the goal of one's spiritual practice in the Buddhist tradition. According to the Buddhist point of view, once we have developed a genuine understanding of the causes of suffering, such as craving and ignorance, then we can completely eradicate these causes and thus be free from suffering.

Fourth truth: path to the cessation of dukkha
While the first three truths are primarily concerned with understanding the nature of dukkha (suffering, anxiety, stress) and its causes, the fourth truth presents a practical method for overcoming dukkha.

The fourth truth would represent the path Sasuke is on to find out the 'truth'.